Calculus Examples

$lim_{x \to 0} \frac{\tan^{2} (2 x)}{x \sin (3 x)}$

Step 1

Apply L'Hospital's rule.

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Step 1.1

Evaluate the limit of the numerator and the limit of the denominator.

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Step 1.1.1

Take the limit of the numerator and the limit of the denominator.

$\frac{lim_{x \to 0} \tan^{2} (2 x)}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2

Evaluate the limit of the numerator.

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Step 1.1.2.1

Evaluate the limit.

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Step 1.1.2.1.1

Move the exponent $2$ from $\tan^{2} (2 x)$ outside the limit using the Limits Power Rule.

$\frac{{(lim_{x \to 0} \tan (2 x))}^{2}}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2.1.2

Move the limit inside the trig function because tangent is continuous.

$\frac{\tan^{2} (lim_{x \to 0} 2 x)}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2.1.3

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$\frac{\tan^{2} (2 lim_{x \to 0} x)}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2.2

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$\frac{\tan^{2} (2 \cdot 0)}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2.3

Simplify the answer.

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Step 1.1.2.3.1

Multiply $2$ by $0$ .

$\frac{\tan^{2} (0)}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2.3.2

The exact value of $\tan (0)$ is $0$ .

$\frac{0^{2}}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.2.3.3

Raising $0$ to any positive power yields $0$ .

$\frac{0}{lim_{x \to 0} x \sin (3 x)}$

Step 1.1.3

Evaluate the limit of the denominator.

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Step 1.1.3.1

Split the limit using the Product of Limits Rule on the limit as $x$ approaches $0$ .

$\frac{0}{lim_{x \to 0} x \cdot lim_{x \to 0} \sin (3 x)}$

Step 1.1.3.2

Move the limit inside the trig function because sine is continuous.

$\frac{0}{lim_{x \to 0} x \cdot \sin (lim_{x \to 0} 3 x)}$

Step 1.1.3.3

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$\frac{0}{lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x)}$

Step 1.1.3.4

Evaluate the limits by plugging in $0$ for all occurrences of $x$ .

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Step 1.1.3.4.1

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$\frac{0}{0 \cdot \sin (3 lim_{x \to 0} x)}$

Step 1.1.3.4.2

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$\frac{0}{0 \cdot \sin (3 \cdot 0)}$

Step 1.1.3.5

Simplify the answer.

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Step 1.1.3.5.1

Multiply $3$ by $0$ .

$\frac{0}{0 \cdot \sin (0)}$

Step 1.1.3.5.2

The exact value of $\sin (0)$ is $0$ .

$\frac{0}{0 \cdot 0}$

Step 1.1.3.5.3

Multiply $0$ by $0$ .

$\frac{0}{0}$

Step 1.1.3.5.4

The expression contains a division by $0$ . The expression is undefined.

Undefined

$\frac{0}{0}$

Step 1.1.3.6

The expression contains a division by $0$ . The expression is undefined.

Undefined

$\frac{0}{0}$

Step 1.1.4

The expression contains a division by $0$ . The expression is undefined.

Undefined

$\frac{0}{0}$

Step 1.2

Since $\frac{0}{0}$ is of indeterminate form, apply L'Hospital's Rule. L'Hospital's Rule states that the limit of a quotient of functions is equal to the limit of the quotient of their derivatives.

$lim_{x \to 0} \frac{\tan^{2} (2 x)}{x \sin (3 x)} = lim_{x \to 0} \frac{\frac{d}{d x} [\tan^{2} (2 x)]}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3

Find the derivative of the numerator and denominator.

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Step 1.3.1

Differentiate the numerator and denominator.

$lim_{x \to 0} \frac{\frac{d}{d x} [\tan^{2} (2 x)]}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{2}$ and $g (x) = \tan (2 x)$ .

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Step 1.3.2.1

To apply the Chain Rule, set $u_{1}$ as $\tan (2 x)$ .

$lim_{x \to 0} \frac{\frac{d}{d u_{1}} [{u_{1}}^{2}] \frac{d}{d x} [\tan (2 x)]}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.2.2

Differentiate using the Power Rule which states that $\frac{d}{d u_{1}} [{u_{1}}^{n}]$ is $n {u_{1}}^{n - 1}$ where $n = 2$ .

$lim_{x \to 0} \frac{2 u_{1} \frac{d}{d x} [\tan (2 x)]}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.2.3

Replace all occurrences of $u_{1}$ with $\tan (2 x)$ .

$lim_{x \to 0} \frac{2 \tan (2 x) \frac{d}{d x} [\tan (2 x)]}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \tan (x)$ and $g (x) = 2 x$ .

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Step 1.3.3.1

To apply the Chain Rule, set $u_{2}$ as $2 x$ .

$lim_{x \to 0} \frac{2 \tan (2 x) (\frac{d}{d u_{2}} [\tan (u_{2})] \frac{d}{d x} [2 x])}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.3.2

The derivative of $\tan (u_{2})$ with respect to $u_{2}$ is $\sec^{2} (u_{2})$ .

$lim_{x \to 0} \frac{2 \tan (2 x) (\sec^{2} (u_{2}) \frac{d}{d x} [2 x])}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.3.3

Replace all occurrences of $u_{2}$ with $2 x$ .

$lim_{x \to 0} \frac{2 \tan (2 x) (\sec^{2} (2 x) \frac{d}{d x} [2 x])}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.4

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$lim_{x \to 0} \frac{2 \tan (2 x) \sec^{2} (2 x) (2 \frac{d}{d x} [x])}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.5

Multiply $2$ by $2$ .

$lim_{x \to 0} \frac{4 \tan (2 x) \sec^{2} (2 x) \frac{d}{d x} [x]}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$lim_{x \to 0} \frac{4 \tan (2 x) \sec^{2} (2 x) \cdot 1}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.7

Multiply $4$ by $1$ .

$lim_{x \to 0} \frac{4 \tan (2 x) \sec^{2} (2 x)}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.8

Reorder the factors of $4 \tan (2 x) \sec^{2} (2 x)$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{\frac{d}{d x} [x \sin (3 x)]}$

Step 1.3.9

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x$ and $g (x) = \sin (3 x)$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x \frac{d}{d x} [\sin (3 x)] + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.10

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = 3 x$ .

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Step 1.3.10.1

To apply the Chain Rule, set $u$ as $3 x$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (\frac{d}{d u} [\sin (u)] \frac{d}{d x} [3 x]) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.10.2

The derivative of $\sin (u)$ with respect to $u$ is $\cos (u)$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (\cos (u) \frac{d}{d x} [3 x]) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.10.3

Replace all occurrences of $u$ with $3 x$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (\cos (3 x) \frac{d}{d x} [3 x]) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.11

Since $3$ is constant with respect to $x$ , the derivative of $3 x$ with respect to $x$ is $3 \frac{d}{d x} [x]$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (\cos (3 x) (3 \frac{d}{d x} [x])) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.12

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (\cos (3 x) (3 \cdot 1)) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.13

Multiply $3$ by $1$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (\cos (3 x) \cdot 3) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.14

Move $3$ to the left of $\cos (3 x)$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (3 \cdot \cos (3 x)) + \sin (3 x) \frac{d}{d x} [x]}$

Step 1.3.15

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (3 \cos (3 x)) + \sin (3 x) \cdot 1}$

Step 1.3.16

Multiply $\sin (3 x)$ by $1$ .

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{x (3 \cos (3 x)) + \sin (3 x)}$

Step 1.3.17

Reorder terms.

$lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan (2 x)}{3 x \cos (3 x) + \sin (3 x)}$

Step 2

Move the term $4$ outside of the limit because it is constant with respect to $x$ .

$4 lim_{x \to 0} \frac{\sec^{2} (2 x) \tan (2 x)}{3 x \cos (3 x) + \sin (3 x)}$

Step 3

Apply L'Hospital's rule.

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Step 3.1

Evaluate the limit of the numerator and the limit of the denominator.

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Step 3.1.1

Take the limit of the numerator and the limit of the denominator.

$4 \frac{lim_{x \to 0} \sec^{2} (2 x) \tan (2 x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2

Evaluate the limit of the numerator.

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Step 3.1.2.1

Split the limit using the Product of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{lim_{x \to 0} \sec^{2} (2 x) \cdot lim_{x \to 0} \tan (2 x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.2

Move the exponent $2$ from $\sec^{2} (2 x)$ outside the limit using the Limits Power Rule.

$4 \frac{{(lim_{x \to 0} \sec (2 x))}^{2} \cdot lim_{x \to 0} \tan (2 x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.3

Move the limit inside the trig function because secant is continuous.

$4 \frac{\sec^{2} (lim_{x \to 0} 2 x) \cdot lim_{x \to 0} \tan (2 x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.4

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{\sec^{2} (2 lim_{x \to 0} x) \cdot lim_{x \to 0} \tan (2 x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.5

Move the limit inside the trig function because tangent is continuous.

$4 \frac{\sec^{2} (2 lim_{x \to 0} x) \cdot \tan (lim_{x \to 0} 2 x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.6

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{\sec^{2} (2 lim_{x \to 0} x) \cdot \tan (2 lim_{x \to 0} x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.7

Evaluate the limits by plugging in $0$ for all occurrences of $x$ .

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Step 3.1.2.7.1

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{\sec^{2} (2 \cdot 0) \cdot \tan (2 lim_{x \to 0} x)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.7.2

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{\sec^{2} (2 \cdot 0) \cdot \tan (2 \cdot 0)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.8

Simplify the answer.

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Step 3.1.2.8.1

Multiply $2$ by $0$ .

$4 \frac{\sec^{2} (0) \cdot \tan (2 \cdot 0)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.8.2

The exact value of $\sec (0)$ is $1$ .

$4 \frac{1^{2} \cdot \tan (2 \cdot 0)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.8.3

One to any power is one.

$4 \frac{1 \cdot \tan (2 \cdot 0)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.8.4

Multiply $\tan (2 \cdot 0)$ by $1$ .

$4 \frac{\tan (2 \cdot 0)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.8.5

Multiply $2$ by $0$ .

$4 \frac{\tan (0)}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.2.8.6

The exact value of $\tan (0)$ is $0$ .

$4 \frac{0}{lim_{x \to 0} 3 x \cos (3 x) + \sin (3 x)}$

Step 3.1.3

Evaluate the limit of the denominator.

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Step 3.1.3.1

Split the limit using the Sum of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{0}{lim_{x \to 0} 3 x \cos (3 x) + lim_{x \to 0} \sin (3 x)}$

Step 3.1.3.2

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{0}{3 lim_{x \to 0} x \cos (3 x) + lim_{x \to 0} \sin (3 x)}$

Step 3.1.3.3

Split the limit using the Product of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{0}{3 lim_{x \to 0} x \cdot lim_{x \to 0} \cos (3 x) + lim_{x \to 0} \sin (3 x)}$

Step 3.1.3.4

Move the limit inside the trig function because cosine is continuous.

$4 \frac{0}{3 lim_{x \to 0} x \cdot \cos (lim_{x \to 0} 3 x) + lim_{x \to 0} \sin (3 x)}$

Step 3.1.3.5

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{0}{3 lim_{x \to 0} x \cdot \cos (3 lim_{x \to 0} x) + lim_{x \to 0} \sin (3 x)}$

Step 3.1.3.6

Move the limit inside the trig function because sine is continuous.

$4 \frac{0}{3 lim_{x \to 0} x \cdot \cos (3 lim_{x \to 0} x) + \sin (lim_{x \to 0} 3 x)}$

Step 3.1.3.7

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{0}{3 lim_{x \to 0} x \cdot \cos (3 lim_{x \to 0} x) + \sin (3 lim_{x \to 0} x)}$

Step 3.1.3.8

Evaluate the limits by plugging in $0$ for all occurrences of $x$ .

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Step 3.1.3.8.1

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{0}{3 \cdot 0 \cdot \cos (3 lim_{x \to 0} x) + \sin (3 lim_{x \to 0} x)}$

Step 3.1.3.8.2

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{0}{3 \cdot 0 \cdot \cos (3 \cdot 0) + \sin (3 lim_{x \to 0} x)}$

Step 3.1.3.8.3

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{0}{3 \cdot 0 \cdot \cos (3 \cdot 0) + \sin (3 \cdot 0)}$

Step 3.1.3.9

Simplify the answer.

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Step 3.1.3.9.1

Simplify each term.

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Step 3.1.3.9.1.1

Multiply $3$ by $0$ .

$4 \frac{0}{0 \cdot \cos (3 \cdot 0) + \sin (3 \cdot 0)}$

Step 3.1.3.9.1.2

Multiply $3$ by $0$ .

$4 \frac{0}{0 \cdot \cos (0) + \sin (3 \cdot 0)}$

Step 3.1.3.9.1.3

The exact value of $\cos (0)$ is $1$ .

$4 \frac{0}{0 \cdot 1 + \sin (3 \cdot 0)}$

Step 3.1.3.9.1.4

Multiply $0$ by $1$ .

$4 \frac{0}{0 + \sin (3 \cdot 0)}$

Step 3.1.3.9.1.5

Multiply $3$ by $0$ .

$4 \frac{0}{0 + \sin (0)}$

Step 3.1.3.9.1.6

The exact value of $\sin (0)$ is $0$ .

$4 \frac{0}{0 + 0}$

Step 3.1.3.9.2

Add $0$ and $0$ .

$4 (\frac{0}{0})$

Step 3.1.3.9.3

The expression contains a division by $0$ . The expression is undefined.

Undefined

$4 (\frac{0}{0})$

Step 3.1.3.10

The expression contains a division by $0$ . The expression is undefined.

Undefined

$4 (\frac{0}{0})$

Step 3.1.4

The expression contains a division by $0$ . The expression is undefined.

Undefined

$4 (\frac{0}{0})$

Step 3.2

Since $\frac{0}{0}$ is of indeterminate form, apply L'Hospital's Rule. L'Hospital's Rule states that the limit of a quotient of functions is equal to the limit of the quotient of their derivatives.

$lim_{x \to 0} \frac{\sec^{2} (2 x) \tan (2 x)}{3 x \cos (3 x) + \sin (3 x)} = lim_{x \to 0} \frac{\frac{d}{d x} [\sec^{2} (2 x) \tan (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3

Find the derivative of the numerator and denominator.

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Step 3.3.1

Differentiate the numerator and denominator.

$4 lim_{x \to 0} \frac{\frac{d}{d x} [\sec^{2} (2 x) \tan (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = \sec^{2} (2 x)$ and $g (x) = \tan (2 x)$ .

$4 lim_{x \to 0} \frac{\sec^{2} (2 x) \frac{d}{d x} [\tan (2 x)] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \tan (x)$ and $g (x) = 2 x$ .

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Step 3.3.3.1

To apply the Chain Rule, set $u_{1}$ as $2 x$ .

$4 lim_{x \to 0} \frac{\sec^{2} (2 x) \frac{d}{d u_{1}} [\tan (u_{1})] \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.3.2

The derivative of $\tan (u_{1})$ with respect to $u_{1}$ is $\sec^{2} (u_{1})$ .

$4 lim_{x \to 0} \frac{\sec^{2} (2 x) \sec^{2} (u_{1}) \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.3.3

Replace all occurrences of $u_{1}$ with $2 x$ .

$4 lim_{x \to 0} \frac{\sec^{2} (2 x) \sec^{2} (2 x) \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.4

Multiply $\sec^{2} (2 x)$ by $\sec^{2} (2 x)$ by adding the exponents.

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Step 3.3.4.1

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$4 lim_{x \to 0} \frac{{\sec (2 x)}^{2 + 2} \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.4.2

Add $2$ and $2$ .

$4 lim_{x \to 0} \frac{\sec^{4} (2 x) \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.5

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$4 lim_{x \to 0} \frac{\sec^{4} (2 x) \cdot 2 \frac{d}{d x} [x] + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$4 lim_{x \to 0} \frac{\sec^{4} (2 x) \cdot 2 \cdot 1 + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.7

Multiply $2$ by $1$ .

$4 lim_{x \to 0} \frac{\sec^{4} (2 x) \cdot 2 + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.8

Move $2$ to the left of $\sec^{4} (2 x)$ .

$4 lim_{x \to 0} \frac{2 \cdot \sec^{4} (2 x) + \tan (2 x) \frac{d}{d x} [\sec^{2} (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.9

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{2}$ and $g (x) = \sec (2 x)$ .

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Step 3.3.9.1

To apply the Chain Rule, set $u_{2}$ as $\sec (2 x)$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + \tan (2 x) \frac{d}{d u_{2}} [{u_{2}}^{2}] \frac{d}{d x} [\sec (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.9.2

Differentiate using the Power Rule which states that $\frac{d}{d u_{2}} [{u_{2}}^{n}]$ is $n {u_{2}}^{n - 1}$ where $n = 2$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + \tan (2 x) \cdot 2 u_{2} \frac{d}{d x} [\sec (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.9.3

Replace all occurrences of $u_{2}$ with $\sec (2 x)$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + \tan (2 x) \cdot 2 \sec (2 x) \frac{d}{d x} [\sec (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.10

Move $2$ to the left of $\tan (2 x)$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \cdot \tan (2 x) \sec (2 x) \frac{d}{d x} [\sec (2 x)]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.11

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sec (x)$ and $g (x) = 2 x$ .

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Step 3.3.11.1

To apply the Chain Rule, set $u_{3}$ as $2 x$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan (2 x) \sec (2 x) \frac{d}{d u_{3}} [\sec (u_{3})] \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.11.2

The derivative of $\sec (u_{3})$ with respect to $u_{3}$ is $\sec (u_{3}) \tan (u_{3})$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan (2 x) \sec (2 x) \sec (u_{3}) \tan (u_{3}) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.11.3

Replace all occurrences of $u_{3}$ with $2 x$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan (2 x) \sec (2 x) \sec (2 x) \tan (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.12

Raise $\tan (2 x)$ to the power of $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{1} (2 x) \tan (2 x) \sec (2 x) \sec (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.13

Raise $\tan (2 x)$ to the power of $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{1} (2 x) \tan^{1} (2 x) \sec (2 x) \sec (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.14

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 {\tan (2 x)}^{1 + 1} \sec (2 x) \sec (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.15

Add $1$ and $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{2} (2 x) \sec (2 x) \sec (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.16

Raise $\sec (2 x)$ to the power of $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{2} (2 x) \sec^{1} (2 x) \sec (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.17

Raise $\sec (2 x)$ to the power of $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{2} (2 x) \sec^{1} (2 x) \sec^{1} (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.18

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{2} (2 x) {\sec (2 x)}^{1 + 1} \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.19

Add $1$ and $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{2} (2 x) \sec^{2} (2 x) \frac{d}{d x} [2 x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.20

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 2 \tan^{2} (2 x) \sec^{2} (2 x) \cdot 2 \frac{d}{d x} [x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.21

Multiply $2$ by $2$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 4 \tan^{2} (2 x) \sec^{2} (2 x) \frac{d}{d x} [x]}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.22

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 4 \tan^{2} (2 x) \sec^{2} (2 x) \cdot 1}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.23

Multiply $4$ by $1$ .

$4 lim_{x \to 0} \frac{2 \sec^{4} (2 x) + 4 \tan^{2} (2 x) \sec^{2} (2 x)}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.24

Reorder terms.

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{\frac{d}{d x} [3 x \cos (3 x) + \sin (3 x)]}$

Step 3.3.25

By the Sum Rule, the derivative of $3 x \cos (3 x) + \sin (3 x)$ with respect to $x$ is $\frac{d}{d x} [3 x \cos (3 x)] + \frac{d}{d x} [\sin (3 x)]$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{\frac{d}{d x} [3 x \cos (3 x)] + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26

Evaluate $\frac{d}{d x} [3 x \cos (3 x)]$ .

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Step 3.3.26.1

Since $3$ is constant with respect to $x$ , the derivative of $3 x \cos (3 x)$ with respect to $x$ is $3 \frac{d}{d x} [x \cos (3 x)]$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 \frac{d}{d x} [x \cos (3 x)] + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x$ and $g (x) = \cos (3 x)$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \frac{d}{d x} [\cos (3 x)] + \cos (3 x) \frac{d}{d x} [x]) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \cos (x)$ and $g (x) = 3 x$ .

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Step 3.3.26.3.1

To apply the Chain Rule, set $u_{1}$ as $3 x$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \frac{d}{d u_{1}} [\cos (u_{1})] \frac{d}{d x} [3 x] + \cos (3 x) \frac{d}{d x} [x]) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.3.2

The derivative of $\cos (u_{1})$ with respect to $u_{1}$ is $- \sin (u_{1})$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 1 \sin (u_{1}) \frac{d}{d x} [3 x] + \cos (3 x) \frac{d}{d x} [x]) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.3.3

Replace all occurrences of $u_{1}$ with $3 x$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 1 \sin (3 x) \frac{d}{d x} [3 x] + \cos (3 x) \frac{d}{d x} [x]) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.4

Since $3$ is constant with respect to $x$ , the derivative of $3 x$ with respect to $x$ is $3 \frac{d}{d x} [x]$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 1 \sin (3 x) \cdot 3 \frac{d}{d x} [x] + \cos (3 x) \frac{d}{d x} [x]) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 1 \sin (3 x) \cdot 3 \cdot 1 + \cos (3 x) \frac{d}{d x} [x]) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 1 \sin (3 x) \cdot 3 \cdot 1 + \cos (3 x) \cdot 1) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.7

Multiply $3$ by $1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 1 \sin (3 x) \cdot 3 + \cos (3 x) \cdot 1) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.8

Multiply $3$ by $- 1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x) \cdot 1) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.26.9

Multiply $\cos (3 x)$ by $1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \frac{d}{d x} [\sin (3 x)]}$

Step 3.3.27

Evaluate $\frac{d}{d x} [\sin (3 x)]$ .

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Step 3.3.27.1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = 3 x$ .

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Step 3.3.27.1.1

To apply the Chain Rule, set $u_{2}$ as $3 x$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \frac{d}{d u_{2}} [\sin (u_{2})] \frac{d}{d x} [3 x]}$

Step 3.3.27.1.2

The derivative of $\sin (u_{2})$ with respect to $u_{2}$ is $\cos (u_{2})$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \cos (u_{2}) \frac{d}{d x} [3 x]}$

Step 3.3.27.1.3

Replace all occurrences of $u_{2}$ with $3 x$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \cos (3 x) \frac{d}{d x} [3 x]}$

Step 3.3.27.2

Since $3$ is constant with respect to $x$ , the derivative of $3 x$ with respect to $x$ is $3 \frac{d}{d x} [x]$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \cos (3 x) \cdot 3 \frac{d}{d x} [x]}$

Step 3.3.27.3

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \cos (3 x) \cdot 3 \cdot 1}$

Step 3.3.27.4

Multiply $3$ by $1$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + \cos (3 x) \cdot 3}$

Step 3.3.27.5

Move $3$ to the left of $\cos (3 x)$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 (x \cdot - 3 \sin (3 x) + \cos (3 x)) + 3 \cos (3 x)}$

Step 3.3.28

Simplify.

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Step 3.3.28.1

Apply the distributive property.

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{3 x \cdot - 3 \sin (3 x) + 3 \cos (3 x) + 3 \cos (3 x)}$

Step 3.3.28.2

Combine terms.

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Step 3.3.28.2.1

Multiply $- 3$ by $3$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{- 9 x \sin (3 x) + 3 \cos (3 x) + 3 \cos (3 x)}$

Step 3.3.28.2.2

Add $3 \cos (3 x)$ and $3 \cos (3 x)$ .

$4 lim_{x \to 0} \frac{4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{- 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4

Evaluate the limit.

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Step 4.1

Split the limit using the Limits Quotient Rule on the limit as $x$ approaches $0$ .

$4 \frac{lim_{x \to 0} 4 \sec^{2} (2 x) \tan^{2} (2 x) + 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.2

Split the limit using the Sum of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{lim_{x \to 0} 4 \sec^{2} (2 x) \tan^{2} (2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.3

Move the term $4$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 lim_{x \to 0} \sec^{2} (2 x) \tan^{2} (2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.4

Split the limit using the Product of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{4 lim_{x \to 0} \sec^{2} (2 x) \cdot lim_{x \to 0} \tan^{2} (2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.5

Move the exponent $2$ from $\sec^{2} (2 x)$ outside the limit using the Limits Power Rule.

$4 \frac{4 {(lim_{x \to 0} \sec (2 x))}^{2} \cdot lim_{x \to 0} \tan^{2} (2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.6

Move the limit inside the trig function because secant is continuous.

$4 \frac{4 \sec^{2} (lim_{x \to 0} 2 x) \cdot lim_{x \to 0} \tan^{2} (2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.7

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot lim_{x \to 0} \tan^{2} (2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.8

Move the exponent $2$ from $\tan^{2} (2 x)$ outside the limit using the Limits Power Rule.

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot {(lim_{x \to 0} \tan (2 x))}^{2} + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.9

Move the limit inside the trig function because tangent is continuous.

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (lim_{x \to 0} 2 x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.10

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + lim_{x \to 0} 2 \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.11

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 lim_{x \to 0} \sec^{4} (2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.12

Move the exponent $4$ from $\sec^{4} (2 x)$ outside the limit using the Limits Power Rule.

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 {(lim_{x \to 0} \sec (2 x))}^{4}}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.13

Move the limit inside the trig function because secant is continuous.

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (lim_{x \to 0} 2 x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.14

Move the term $2$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{lim_{x \to 0} - 9 x \sin (3 x) + 6 \cos (3 x)}$

Step 4.15

Split the limit using the Sum of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- lim_{x \to 0} 9 x \sin (3 x) + lim_{x \to 0} 6 \cos (3 x)}$

Step 4.16

Move the term $9$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \sin (3 x) + lim_{x \to 0} 6 \cos (3 x)}$

Step 4.17

Split the limit using the Product of Limits Rule on the limit as $x$ approaches $0$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot lim_{x \to 0} \sin (3 x) + lim_{x \to 0} 6 \cos (3 x)}$

Step 4.18

Move the limit inside the trig function because sine is continuous.

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (lim_{x \to 0} 3 x) + lim_{x \to 0} 6 \cos (3 x)}$

Step 4.19

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + lim_{x \to 0} 6 \cos (3 x)}$

Step 4.20

Move the term $6$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + 6 lim_{x \to 0} \cos (3 x)}$

Step 4.21

Move the limit inside the trig function because cosine is continuous.

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + 6 \cos (lim_{x \to 0} 3 x)}$

Step 4.22

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$4 \frac{4 \sec^{2} (2 lim_{x \to 0} x) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + 6 \cos (3 lim_{x \to 0} x)}$

Step 5

Evaluate the limits by plugging in $0$ for all occurrences of $x$ .

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Step 5.1

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{4 \sec^{2} (2 \cdot 0) \cdot \tan^{2} (2 lim_{x \to 0} x) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + 6 \cos (3 lim_{x \to 0} x)}$

Step 5.2

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{4 \sec^{2} (2 \cdot 0) \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 lim_{x \to 0} x)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + 6 \cos (3 lim_{x \to 0} x)}$

Step 5.3

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{4 \sec^{2} (2 \cdot 0) \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 lim_{x \to 0} x \cdot \sin (3 lim_{x \to 0} x) + 6 \cos (3 lim_{x \to 0} x)}$

Step 5.4

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{4 \sec^{2} (2 \cdot 0) \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 lim_{x \to 0} x) + 6 \cos (3 lim_{x \to 0} x)}$

Step 5.5

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{4 \sec^{2} (2 \cdot 0) \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 lim_{x \to 0} x)}$

Step 5.6

Evaluate the limit of $x$ by plugging in $0$ for $x$ .

$4 \frac{4 \sec^{2} (2 \cdot 0) \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6

Simplify the answer.

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Step 6.1

Simplify the numerator.

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Step 6.1.1

Multiply $2$ by $0$ .

$4 \frac{4 \sec^{2} (0) \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.2

The exact value of $\sec (0)$ is $1$ .

$4 \frac{4 \cdot 1^{2} \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.3

One to any power is one.

$4 \frac{4 \cdot 1 \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.4

Multiply $4$ by $1$ .

$4 \frac{4 \cdot \tan^{2} (2 \cdot 0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.5

Multiply $2$ by $0$ .

$4 \frac{4 \cdot \tan^{2} (0) + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.6

The exact value of $\tan (0)$ is $0$ .

$4 \frac{4 \cdot 0^{2} + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.7

Raising $0$ to any positive power yields $0$ .

$4 \frac{4 \cdot 0 + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.8

Multiply $4$ by $0$ .

$4 \frac{0 + 2 \sec^{4} (2 \cdot 0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.9

Multiply $2$ by $0$ .

$4 \frac{0 + 2 \sec^{4} (0)}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.10

The exact value of $\sec (0)$ is $1$ .

$4 \frac{0 + 2 \cdot 1^{4}}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.11

One to any power is one.

$4 \frac{0 + 2 \cdot 1}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.12

Multiply $2$ by $1$ .

$4 \frac{0 + 2}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.1.13

Add $0$ and $2$ .

$4 \frac{2}{- 9 \cdot 0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.2

Simplify the denominator.

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Step 6.2.1

Multiply $- 9$ by $0$ .

$4 \frac{2}{0 \cdot \sin (3 \cdot 0) + 6 \cos (3 \cdot 0)}$

Step 6.2.2

Multiply $3$ by $0$ .

$4 \frac{2}{0 \cdot \sin (0) + 6 \cos (3 \cdot 0)}$

Step 6.2.3

The exact value of $\sin (0)$ is $0$ .

$4 \frac{2}{0 \cdot 0 + 6 \cos (3 \cdot 0)}$

Step 6.2.4

Multiply $0$ by $0$ .

$4 \frac{2}{0 + 6 \cos (3 \cdot 0)}$

Step 6.2.5

Multiply $3$ by $0$ .

$4 \frac{2}{0 + 6 \cos (0)}$

Step 6.2.6

The exact value of $\cos (0)$ is $1$ .

$4 \frac{2}{0 + 6 \cdot 1}$

Step 6.2.7

Multiply $6$ by $1$ .

$4 \frac{2}{0 + 6}$

Step 6.2.8

Add $0$ and $6$ .

$4 (\frac{2}{6})$

Step 6.3

Cancel the common factor of $2$ and $6$ .

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Step 6.3.1

Factor $2$ out of $2$ .

$4 \frac{2 (1)}{6}$

Step 6.3.2

Cancel the common factors.

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Step 6.3.2.1

Factor $2$ out of $6$ .

$4 \frac{2 \cdot 1}{2 \cdot 3}$

Step 6.3.2.2

Cancel the common factor.

$4 \frac{2 \cdot 1}{2 \cdot 3}$

Step 6.3.2.3

Rewrite the expression.

$4 (\frac{1}{3})$

Step 6.4

Combine $4$ and $\frac{1}{3}$ .

$\frac{4}{3}$

Step 7

The result can be shown in multiple forms.

Exact Form:

$\frac{4}{3}$

Decimal Form:

$1.\overline{3}$