Calculus Examples

$lim_{x \to 0} \frac{{(3 + x)}^{4} - 81}{6 x}$

Step 1

Move the term $\frac{1}{6}$ outside of the limit because it is constant with respect to $x$ .

$\frac{1}{6} lim_{x \to 0} \frac{{(3 + x)}^{4} - 81}{x}$

Step 2

Apply L'Hospital's rule.

Tap for more steps...

Step 2.1

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

Tap for more steps...

Step 2.1.1

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

$\frac{1}{6} \cdot \frac{lim_{x \to 0} {(3 + x)}^{4} - 81}{lim_{x \to 0} x}$

Step 2.1.2

Evaluate the limit of the numerator.

Tap for more steps...

Step 2.1.2.1

Evaluate the limit.

Tap for more steps...

Step 2.1.2.1.1

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

$\frac{1}{6} \cdot \frac{lim_{x \to 0} {(3 + x)}^{4} - lim_{x \to 0} 81}{lim_{x \to 0} x}$

Step 2.1.2.1.2

Move the exponent $4$ from ${(3 + x)}^{4}$ outside the limit using the Limits Power Rule.

$\frac{1}{6} \cdot \frac{{(lim_{x \to 0} 3 + x)}^{4} - lim_{x \to 0} 81}{lim_{x \to 0} x}$

Step 2.1.2.1.3

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

$\frac{1}{6} \cdot \frac{{(lim_{x \to 0} 3 + lim_{x \to 0} x)}^{4} - lim_{x \to 0} 81}{lim_{x \to 0} x}$

Step 2.1.2.1.4

Evaluate the limit of $3$ which is constant as $x$ approaches $0$ .

$\frac{1}{6} \cdot \frac{{(3 + lim_{x \to 0} x)}^{4} - lim_{x \to 0} 81}{lim_{x \to 0} x}$

Step 2.1.2.1.5

Evaluate the limit of $81$ which is constant as $x$ approaches $0$ .

$\frac{1}{6} \cdot \frac{{(3 + lim_{x \to 0} x)}^{4} - 1 \cdot 81}{lim_{x \to 0} x}$

Step 2.1.2.2

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

$\frac{1}{6} \cdot \frac{{(3 + 0)}^{4} - 1 \cdot 81}{lim_{x \to 0} x}$

Step 2.1.2.3

Simplify the answer.

Tap for more steps...

Step 2.1.2.3.1

Simplify each term.

Tap for more steps...

Step 2.1.2.3.1.1

Add $3$ and $0$ .

$\frac{1}{6} \cdot \frac{3^{4} - 1 \cdot 81}{lim_{x \to 0} x}$

Step 2.1.2.3.1.2

Raise $3$ to the power of $4$ .

$\frac{1}{6} \cdot \frac{81 - 1 \cdot 81}{lim_{x \to 0} x}$

Step 2.1.2.3.1.3

Multiply $- 1$ by $81$ .

$\frac{1}{6} \cdot \frac{81 - 81}{lim_{x \to 0} x}$

Step 2.1.2.3.2

Subtract $81$ from $81$ .

$\frac{1}{6} \cdot \frac{0}{lim_{x \to 0} x}$

Step 2.1.3

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

$\frac{1}{6} \cdot \frac{0}{0}$

Step 2.1.4

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

Undefined

$\frac{1}{6} \cdot \frac{0}{0}$

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.

$lim_{x \to 0} \frac{{(3 + x)}^{4} - 81}{x} = lim_{x \to 0} \frac{\frac{d}{d x} [{(3 + x)}^{4} - 81]}{\frac{d}{d x} [x]}$

Step 2.3

Find the derivative of the numerator and denominator.

Tap for more steps...

Step 2.3.1

Differentiate the numerator and denominator.

$\frac{1}{6} lim_{x \to 0} \frac{\frac{d}{d x} [{(3 + x)}^{4} - 81]}{\frac{d}{d x} [x]}$

Step 2.3.2

By the Sum Rule, the derivative of ${(3 + x)}^{4} - 81$ with respect to $x$ is $\frac{d}{d x} [{(3 + x)}^{4}] + \frac{d}{d x} [- 81]$ .

$\frac{1}{6} lim_{x \to 0} \frac{\frac{d}{d x} [{(3 + x)}^{4}] + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3

Evaluate $\frac{d}{d x} [{(3 + x)}^{4}]$ .

Tap for more steps...

Step 2.3.3.1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{4}$ and $g (x) = 3 + x$ .

Tap for more steps...

Step 2.3.3.1.1

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

$\frac{1}{6} lim_{x \to 0} \frac{\frac{d}{d u} [u^{4}] \frac{d}{d x} [3 + x] + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.1.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 4$ .

$\frac{1}{6} lim_{x \to 0} \frac{4 u^{3} \frac{d}{d x} [3 + x] + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.1.3

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

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} \frac{d}{d x} [3 + x] + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.2

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

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} (\frac{d}{d x} [3] + \frac{d}{d x} [x]) + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.3

Since $3$ is constant with respect to $x$ , the derivative of $3$ with respect to $x$ is $0$ .

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} (0 + \frac{d}{d x} [x]) + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.4

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

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} (0 + 1) + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.5

Add $0$ and $1$ .

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} \cdot 1 + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.3.6

Multiply $4$ by $1$ .

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} + \frac{d}{d x} [- 81]}{\frac{d}{d x} [x]}$

Step 2.3.4

Since $- 81$ is constant with respect to $x$ , the derivative of $- 81$ with respect to $x$ is $0$ .

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3} + 0}{\frac{d}{d x} [x]}$

Step 2.3.5

Add $4 {(3 + x)}^{3}$ and $0$ .

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3}}{\frac{d}{d x} [x]}$

Step 2.3.6

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

$\frac{1}{6} lim_{x \to 0} \frac{4 {(3 + x)}^{3}}{1}$

Step 2.4

Divide $4 {(3 + x)}^{3}$ by $1$ .

$\frac{1}{6} lim_{x \to 0} 4 {(3 + x)}^{3}$

Step 3

Evaluate the limit.

Tap for more steps...

Step 3.1

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

$\frac{1}{6} \cdot 4 lim_{x \to 0} {(3 + x)}^{3}$

Step 3.2

Move the exponent $3$ from ${(3 + x)}^{3}$ outside the limit using the Limits Power Rule.

$\frac{1}{6} \cdot 4 {(lim_{x \to 0} 3 + x)}^{3}$

Step 3.3

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

$\frac{1}{6} \cdot 4 {(lim_{x \to 0} 3 + lim_{x \to 0} x)}^{3}$

Step 3.4

Evaluate the limit of $3$ which is constant as $x$ approaches $0$ .

$\frac{1}{6} \cdot 4 {(3 + lim_{x \to 0} x)}^{3}$

Step 4

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

$\frac{1}{6} \cdot 4 {(3 + 0)}^{3}$

Step 5

Simplify the answer.

Tap for more steps...

Step 5.1

Cancel the common factor of $2$ .

Tap for more steps...

Step 5.1.1

Factor $2$ out of $6$ .

$\frac{1}{2 (3)} \cdot 4 {(3 + 0)}^{3}$

Step 5.1.2

Factor $2$ out of $4$ .

$\frac{1}{2 \cdot 3} \cdot (2 \cdot 2) {(3 + 0)}^{3}$

Step 5.1.3

Cancel the common factor.

$\frac{1}{2 \cdot 3} \cdot (2 \cdot 2) {(3 + 0)}^{3}$

Step 5.1.4

Rewrite the expression.

$\frac{1}{3} \cdot 2 {(3 + 0)}^{3}$

Step 5.2

Combine $\frac{1}{3}$ and $2$ .

$\frac{2}{3} {(3 + 0)}^{3}$

Step 5.3

Add $3$ and $0$ .

$\frac{2}{3} \cdot 3^{3}$

Step 5.4

Cancel the common factor of $3$ .

Tap for more steps...

Step 5.4.1

Factor $3$ out of $3^{3}$ .

$\frac{2}{3} \cdot (3 \cdot 3^{2})$

Step 5.4.2

Cancel the common factor.

$\frac{2}{3} \cdot (3 \cdot 3^{2})$

Step 5.4.3

Rewrite the expression.

$2 \cdot 3^{2}$

Step 5.5

Raise $3$ to the power of $2$ .

$2 \cdot 9$

Step 5.6

Multiply $2$ by $9$ .

$18$