Calculus Examples

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

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.

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

Step 1.1.2

Evaluate the limit of the numerator.

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Step 1.1.2.1

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

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

Step 1.1.2.2

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

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

Step 1.1.2.3

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

$\frac{0}{lim_{x \to 0} 2 x^{2} - x}$

Step 1.1.3

Evaluate the limit of the denominator.

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Step 1.1.3.1

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

$\frac{0}{lim_{x \to 0} 2 x^{2} - lim_{x \to 0} x}$

Step 1.1.3.2

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

$\frac{0}{2 lim_{x \to 0} x^{2} - lim_{x \to 0} x}$

Step 1.1.3.3

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

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

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 $x$ .

$\frac{0}{2 \cdot 0^{2} - lim_{x \to 0} x}$

Step 1.1.3.4.2

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

$\frac{0}{2 \cdot 0^{2} + 0}$

Step 1.1.3.5

Simplify the answer.

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Step 1.1.3.5.1

Simplify each term.

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Step 1.1.3.5.1.1

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

$\frac{0}{2 \cdot 0 + 0}$

Step 1.1.3.5.1.2

Multiply $2$ by $0$ .

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

Step 1.1.3.5.2

Add $0$ and $0$ .

$\frac{0}{0}$

Step 1.1.3.5.3

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.

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

Step 1.3

Find the derivative of the numerator and denominator.

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Step 1.3.1

Differentiate the numerator and denominator.

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

Step 1.3.2

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

$lim_{x \to 0} \frac{\cos (x)}{\frac{d}{d x} [2 x^{2} - x]}$

Step 1.3.3

By the Sum Rule, the derivative of $2 x^{2} - x$ with respect to $x$ is $\frac{d}{d x} [2 x^{2}] + \frac{d}{d x} [- x]$ .

$lim_{x \to 0} \frac{\cos (x)}{\frac{d}{d x} [2 x^{2}] + \frac{d}{d x} [- x]}$

Step 1.3.4

Evaluate $\frac{d}{d x} [2 x^{2}]$ .

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Step 1.3.4.1

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

$lim_{x \to 0} \frac{\cos (x)}{2 \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- x]}$

Step 1.3.4.2

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

$lim_{x \to 0} \frac{\cos (x)}{2 (2 x) + \frac{d}{d x} [- x]}$

Step 1.3.4.3

Multiply $2$ by $2$ .

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

Step 1.3.5

Evaluate $\frac{d}{d x} [- x]$ .

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Step 1.3.5.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

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

Step 1.3.5.2

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

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

Step 1.3.5.3

Multiply $- 1$ by $1$ .

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

Step 2

Evaluate the limit.

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Step 2.1

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

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

Step 2.2

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

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

Step 2.3

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

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

Step 2.4

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

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

Step 2.5

Evaluate the limit of $1$ which is constant as $x$ approaches $0$ .

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

Step 3

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

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Step 3.1

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

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

Step 3.2

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

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

Step 4

Simplify the answer.

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Step 4.1

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

$\frac{1}{4 \cdot 0 - 1 \cdot 1}$

Step 4.2

Simplify the denominator.

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Step 4.2.1

Multiply $4$ by $0$ .

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

Step 4.2.2

Multiply $- 1$ by $1$ .

$\frac{1}{0 - 1}$

Step 4.2.3

Subtract $1$ from $0$ .

$\frac{1}{- 1}$

Step 4.3

Divide $1$ by $- 1$ .

$- 1$