Calculus Examples

$lim_{x \to 0} \frac{\sin (4 x)}{9 x}$

Step 1

Move the term $\frac{1}{9}$ outside of the limit because it is constant with respect to $x$ .

$\frac{1}{9} lim_{x \to 0} \frac{\sin (4 x)}{x}$

Step 2

Apply L'Hospital's rule.

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Step 2.1

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

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Step 2.1.1

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

$\frac{1}{9} \cdot \frac{lim_{x \to 0} \sin (4 x)}{lim_{x \to 0} x}$

Step 2.1.2

Evaluate the limit of the numerator.

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Step 2.1.2.1

Evaluate the limit.

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Step 2.1.2.1.1

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

$\frac{1}{9} \cdot \frac{\sin (lim_{x \to 0} 4 x)}{lim_{x \to 0} x}$

Step 2.1.2.1.2

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

$\frac{1}{9} \cdot \frac{\sin (4 lim_{x \to 0} x)}{lim_{x \to 0} x}$

Step 2.1.2.2

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

$\frac{1}{9} \cdot \frac{\sin (4 \cdot 0)}{lim_{x \to 0} x}$

Step 2.1.2.3

Simplify the answer.

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Step 2.1.2.3.1

Multiply $4$ by $0$ .

$\frac{1}{9} \cdot \frac{\sin (0)}{lim_{x \to 0} x}$

Step 2.1.2.3.2

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

$\frac{1}{9} \cdot \frac{0}{lim_{x \to 0} x}$

Step 2.1.3

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

$\frac{1}{9} \cdot \frac{0}{0}$

Step 2.1.4

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

Undefined

$\frac{1}{9} \cdot \frac{0}{0}$

Step 2.2

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.

$lim_{x \to 0} \frac{\sin (4 x)}{x} = lim_{x \to 0} \frac{\frac{d}{d x} [\sin (4 x)]}{\frac{d}{d x} [x]}$

Step 2.3

Find the derivative of the numerator and denominator.

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Step 2.3.1

Differentiate the numerator and denominator.

$\frac{1}{9} lim_{x \to 0} \frac{\frac{d}{d x} [\sin (4 x)]}{\frac{d}{d x} [x]}$

Step 2.3.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = 4 x$ .

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Step 2.3.2.1

To apply the Chain Rule, set $u$ as $4 x$ .

$\frac{1}{9} lim_{x \to 0} \frac{\frac{d}{d u} [\sin (u)] \frac{d}{d x} [4 x]}{\frac{d}{d x} [x]}$

Step 2.3.2.2

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

$\frac{1}{9} lim_{x \to 0} \frac{\cos (u) \frac{d}{d x} [4 x]}{\frac{d}{d x} [x]}$

Step 2.3.2.3

Replace all occurrences of $u$ with $4 x$ .

$\frac{1}{9} lim_{x \to 0} \frac{\cos (4 x) \frac{d}{d x} [4 x]}{\frac{d}{d x} [x]}$

Step 2.3.3

Since $4$ is constant with respect to $x$ , the derivative of $4 x$ with respect to $x$ is $4 \frac{d}{d x} [x]$ .

$\frac{1}{9} lim_{x \to 0} \frac{\cos (4 x) \cdot 4 \frac{d}{d x} [x]}{\frac{d}{d x} [x]}$

Step 2.3.4

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

$\frac{1}{9} lim_{x \to 0} \frac{\cos (4 x) \cdot 4 \cdot 1}{\frac{d}{d x} [x]}$

Step 2.3.5

Multiply $4$ by $1$ .

$\frac{1}{9} lim_{x \to 0} \frac{\cos (4 x) \cdot 4}{\frac{d}{d x} [x]}$

Step 2.3.6

Move $4$ to the left of $\cos (4 x)$ .

$\frac{1}{9} lim_{x \to 0} \frac{4 \cdot \cos (4 x)}{\frac{d}{d x} [x]}$

Step 2.3.7

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

$\frac{1}{9} lim_{x \to 0} \frac{4 \cos (4 x)}{1}$

Step 2.4

Divide $4 \cos (4 x)$ by $1$ .

$\frac{1}{9} lim_{x \to 0} 4 \cos (4 x)$

Step 3

Evaluate the limit.

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Step 3.1

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

$\frac{1}{9} \cdot 4 lim_{x \to 0} \cos (4 x)$

Step 3.2

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

$\frac{1}{9} \cdot 4 \cos (lim_{x \to 0} 4 x)$

Step 3.3

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

$\frac{1}{9} \cdot 4 \cos (4 lim_{x \to 0} x)$

Step 4

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

$\frac{1}{9} \cdot 4 \cos (4 \cdot 0)$

Step 5

Simplify the answer.

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Step 5.1

Combine $\frac{1}{9}$ and $4$ .

$\frac{4}{9} \cos (4 \cdot 0)$

Step 5.2

Multiply $4$ by $0$ .

$\frac{4}{9} \cos (0)$

Step 5.3

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

$\frac{4}{9} \cdot 1$

Step 5.4

Multiply $\frac{4}{9}$ by $1$ .

$\frac{4}{9}$

Step 6

The result can be shown in multiple forms.

Exact Form:

$\frac{4}{9}$

Decimal Form:

$0.\overline{4}$