Calculus Examples

$y = \ln (7 - 8 x)$

Step 1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \ln (x)$ and $g (x) = 7 - 8 x$ .

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Step 1.1

To apply the Chain Rule, set $u$ as $7 - 8 x$ .

$\frac{d}{d u} [\ln (u)] \frac{d}{d x} [7 - 8 x]$

Step 1.2

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

$\frac{1}{u} \frac{d}{d x} [7 - 8 x]$

Step 1.3

Replace all occurrences of $u$ with $7 - 8 x$ .

$\frac{1}{7 - 8 x} \frac{d}{d x} [7 - 8 x]$

Step 2

Differentiate.

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Step 2.1

By the Sum Rule, the derivative of $7 - 8 x$ with respect to $x$ is $\frac{d}{d x} [7] + \frac{d}{d x} [- 8 x]$ .

$\frac{1}{7 - 8 x} (\frac{d}{d x} [7] + \frac{d}{d x} [- 8 x])$

Step 2.2

Since $7$ is constant with respect to $x$ , the derivative of $7$ with respect to $x$ is $0$ .

$\frac{1}{7 - 8 x} (0 + \frac{d}{d x} [- 8 x])$

Step 2.3

Add $0$ and $\frac{d}{d x} [- 8 x]$ .

$\frac{1}{7 - 8 x} \frac{d}{d x} [- 8 x]$

Step 2.4

Since $- 8$ is constant with respect to $x$ , the derivative of $- 8 x$ with respect to $x$ is $- 8 \frac{d}{d x} [x]$ .

$\frac{1}{7 - 8 x} (- 8 \frac{d}{d x} [x])$

Step 2.5

Combine fractions.

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Step 2.5.1

Combine $- 8$ and $\frac{1}{7 - 8 x}$ .

$\frac{- 8}{7 - 8 x} \frac{d}{d x} [x]$

Step 2.5.2

Move the negative in front of the fraction.

$- \frac{8}{7 - 8 x} \frac{d}{d x} [x]$

Step 2.6

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

$- \frac{8}{7 - 8 x} \cdot 1$

Step 2.7

Multiply $- 1$ by $1$ .

$- \frac{8}{7 - 8 x}$