Calculus Examples

$f (x) = \log_{8} (\frac{x^{2} - 5}{x - 10})$

Step 1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \log_{8} (x)$ and $g (x) = \frac{x^{2} - 5}{x - 10}$ .

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Step 1.1

To apply the Chain Rule, set $u$ as $\frac{x^{2} - 5}{x - 10}$ .

$\frac{d}{d u} [\log_{8} (u)] \frac{d}{d x} [\frac{x^{2} - 5}{x - 10}]$

Step 1.2

The derivative of $\log_{8} (u)$ with respect to $u$ is $\frac{1}{u \ln (8)}$ .

$\frac{1}{u \ln (8)} \frac{d}{d x} [\frac{x^{2} - 5}{x - 10}]$

Step 1.3

Replace all occurrences of $u$ with $\frac{x^{2} - 5}{x - 10}$ .

$\frac{1}{\frac{x^{2} - 5}{x - 10} \ln (8)} \frac{d}{d x} [\frac{x^{2} - 5}{x - 10}]$

Step 2

Combine $\frac{x^{2} - 5}{x - 10}$ and $\ln (8)$ .

$\frac{1}{\frac{(x^{2} - 5) \ln (8)}{x - 10}} \frac{d}{d x} [\frac{x^{2} - 5}{x - 10}]$

Step 3

Multiply by the reciprocal of the fraction to divide by $\frac{(x^{2} - 5) \ln (8)}{x - 10}$ .

$1 \frac{x - 10}{(x^{2} - 5) \ln (8)} \frac{d}{d x} [\frac{x^{2} - 5}{x - 10}]$

Step 4

Multiply $\frac{x - 10}{(x^{2} - 5) \ln (8)}$ by $1$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \frac{d}{d x} [\frac{x^{2} - 5}{x - 10}]$

Step 5

Differentiate using the Quotient Rule which states that $\frac{d}{d x} [\frac{f (x)}{g (x)}]$ is $\frac{g (x) \frac{d}{d x} [f (x)] - f (x) \frac{d}{d x} [g (x)]}{{g (x)}^{2}}$ where $f (x) = x^{2} - 5$ and $g (x) = x - 10$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{(x - 10) \frac{d}{d x} [x^{2} - 5] - (x^{2} - 5) \frac{d}{d x} [x - 10]}{{(x - 10)}^{2}}$

Step 6

Differentiate.

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Step 6.1

By the Sum Rule, the derivative of $x^{2} - 5$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 5]$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{(x - 10) (\frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 5]) - (x^{2} - 5) \frac{d}{d x} [x - 10]}{{(x - 10)}^{2}}$

Step 6.2

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

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{(x - 10) (2 x + \frac{d}{d x} [- 5]) - (x^{2} - 5) \frac{d}{d x} [x - 10]}{{(x - 10)}^{2}}$

Step 6.3

Since $- 5$ is constant with respect to $x$ , the derivative of $- 5$ with respect to $x$ is $0$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{(x - 10) (2 x + 0) - (x^{2} - 5) \frac{d}{d x} [x - 10]}{{(x - 10)}^{2}}$

Step 6.4

Simplify the expression.

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Step 6.4.1

Add $2 x$ and $0$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{(x - 10) (2 x) - (x^{2} - 5) \frac{d}{d x} [x - 10]}{{(x - 10)}^{2}}$

Step 6.4.2

Move $2$ to the left of $x - 10$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{2 \cdot (x - 10) x - (x^{2} - 5) \frac{d}{d x} [x - 10]}{{(x - 10)}^{2}}$

Step 6.5

By the Sum Rule, the derivative of $x - 10$ with respect to $x$ is $\frac{d}{d x} [x] + \frac{d}{d x} [- 10]$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{2 (x - 10) x - (x^{2} - 5) (\frac{d}{d x} [x] + \frac{d}{d x} [- 10])}{{(x - 10)}^{2}}$

Step 6.6

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

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{2 (x - 10) x - (x^{2} - 5) (1 + \frac{d}{d x} [- 10])}{{(x - 10)}^{2}}$

Step 6.7

Since $- 10$ is constant with respect to $x$ , the derivative of $- 10$ with respect to $x$ is $0$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{2 (x - 10) x - (x^{2} - 5) (1 + 0)}{{(x - 10)}^{2}}$

Step 6.8

Combine fractions.

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Step 6.8.1

Add $1$ and $0$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{2 (x - 10) x - (x^{2} - 5) \cdot 1}{{(x - 10)}^{2}}$

Step 6.8.2

Multiply $- 1$ by $1$ .

$\frac{x - 10}{(x^{2} - 5) \ln (8)} \cdot \frac{2 (x - 10) x - (x^{2} - 5)}{{(x - 10)}^{2}}$

Step 6.8.3

Multiply $\frac{x - 10}{(x^{2} - 5) \ln (8)}$ by $\frac{2 (x - 10) x - (x^{2} - 5)}{{(x - 10)}^{2}}$ .

$\frac{(x - 10) (2 (x - 10) x - (x^{2} - 5))}{(x^{2} - 5) \ln (8) {(x - 10)}^{2}}$

Step 7

Cancel the common factors.

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Step 7.1

Factor $x - 10$ out of $(x^{2} - 5) \ln (8) {(x - 10)}^{2}$ .

$\frac{(x - 10) (2 (x - 10) x - (x^{2} - 5))}{(x - 10) ((x^{2} - 5) \ln (8) (x - 10))}$

Step 7.2

Cancel the common factor.

$\frac{(x - 10) (2 (x - 10) x - (x^{2} - 5))}{(x - 10) ((x^{2} - 5) \ln (8) (x - 10))}$

Step 7.3

Rewrite the expression.

$\frac{2 (x - 10) x - (x^{2} - 5)}{(x^{2} - 5) \ln (8) (x - 10)}$

Step 8

Simplify.

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Step 8.1

Apply the distributive property.

$\frac{(2 x + 2 \cdot - 10) x - (x^{2} - 5)}{(x^{2} - 5) \ln (8) (x - 10)}$

Step 8.2

Apply the distributive property.

$\frac{2 x \cdot x + 2 \cdot - 10 x - (x^{2} - 5)}{(x^{2} - 5) \ln (8) (x - 10)}$

Step 8.3

Apply the distributive property.

$\frac{2 x \cdot x + 2 \cdot - 10 x - x^{2} - - 5}{(x^{2} - 5) \ln (8) (x - 10)}$

Step 8.4

Apply the distributive property.

$\frac{2 x \cdot x + 2 \cdot - 10 x - x^{2} - - 5}{(x^{2} \ln (8) - 5 \ln (8)) (x - 10)}$

Step 8.5

Simplify the numerator.

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Step 8.5.1

Simplify each term.

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Step 8.5.1.1

Multiply $x$ by $x$ by adding the exponents.

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Step 8.5.1.1.1

Move $x$ .

$\frac{2 (x \cdot x) + 2 \cdot - 10 x - x^{2} - - 5}{(x^{2} \ln (8) - 5 \ln (8)) (x - 10)}$

Step 8.5.1.1.2

Multiply $x$ by $x$ .

$\frac{2 x^{2} + 2 \cdot - 10 x - x^{2} - - 5}{(x^{2} \ln (8) - 5 \ln (8)) (x - 10)}$

Step 8.5.1.2

Multiply $2$ by $- 10$ .

$\frac{2 x^{2} - 20 x - x^{2} - - 5}{(x^{2} \ln (8) - 5 \ln (8)) (x - 10)}$

Step 8.5.1.3

Multiply $- 1$ by $- 5$ .

$\frac{2 x^{2} - 20 x - x^{2} + 5}{(x^{2} \ln (8) - 5 \ln (8)) (x - 10)}$

Step 8.5.2

Subtract $x^{2}$ from $2 x^{2}$ .

$\frac{x^{2} - 20 x + 5}{(x^{2} \ln (8) - 5 \ln (8)) (x - 10)}$

Step 8.6

Reorder terms.

$\frac{x^{2} - 20 x + 5}{(x - 10) (x^{2} \ln (8) - 5 \ln (8))}$