Calculus Examples

$f (x) = \ln (4 + 5 x)$

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 $g (x) = 4 + 5 x$ .

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Step 1.1

To apply the Chain Rule, set $u$ as $4 + 5 x$ .

$\frac{d}{d u} [\ln (u)] \frac{d}{d x} [4 + 5 x]$

Step 1.2

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

$\frac{1}{u} \frac{d}{d x} [4 + 5 x]$

Step 1.3

Replace all occurrences of $u$ with $4 + 5 x$ .

$\frac{1}{4 + 5 x} \frac{d}{d x} [4 + 5 x]$

Step 2

Differentiate.

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Step 2.1

By the Sum Rule, the derivative of $4 + 5 x$ with respect to $x$ is $\frac{d}{d x} [4] + \frac{d}{d x} [5 x]$ .

$\frac{1}{4 + 5 x} (\frac{d}{d x} [4] + \frac{d}{d x} [5 x])$

Step 2.2

Since $4$ is constant with respect to $x$ , the derivative of $4$ with respect to $x$ is $0$ .

$\frac{1}{4 + 5 x} (0 + \frac{d}{d x} [5 x])$

Step 2.3

Add $0$ and $\frac{d}{d x} [5 x]$ .

$\frac{1}{4 + 5 x} \frac{d}{d x} [5 x]$

Step 2.4

Since $5$ is constant with respect to $x$ , the derivative of $5 x$ with respect to $x$ is $5 \frac{d}{d x} [x]$ .

$\frac{1}{4 + 5 x} (5 \frac{d}{d x} [x])$

Step 2.5

Combine $5$ and $\frac{1}{4 + 5 x}$ .

$\frac{5}{4 + 5 x} \frac{d}{d x} [x]$

Step 2.6

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

$\frac{5}{4 + 5 x} \cdot 1$

Step 2.7

Simplify the expression.

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Step 2.7.1

Multiply $\frac{5}{4 + 5 x}$ by $1$ .

$\frac{5}{4 + 5 x}$

Step 2.7.2

Reorder terms.

$\frac{5}{5 x + 4}$