Calculus Examples

$y = e^{6 x} \cos (x)$

Step 1

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = e^{6 x}$ and $g (x) = \cos (x)$ .

$e^{6 x} \frac{d}{d x} [\cos (x)] + \cos (x) \frac{d}{d x} [e^{6 x}]$

Step 2

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

$e^{6 x} (- \sin (x)) + \cos (x) \frac{d}{d x} [e^{6 x}]$

Step 3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = 6 x$ .

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Step 3.1

To apply the Chain Rule, set $u$ as $6 x$ .

$e^{6 x} (- \sin (x)) + \cos (x) (\frac{d}{d u} [e^{u}] \frac{d}{d x} [6 x])$

Step 3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u} [a^{u}]$ is $a^{u} \ln (a)$ where $a$ = $e$ .

$e^{6 x} (- \sin (x)) + \cos (x) (e^{u} \frac{d}{d x} [6 x])$

Step 3.3

Replace all occurrences of $u$ with $6 x$ .

$e^{6 x} (- \sin (x)) + \cos (x) (e^{6 x} \frac{d}{d x} [6 x])$

Step 4

Differentiate.

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Step 4.1

Since $6$ is constant with respect to $x$ , the derivative of $6 x$ with respect to $x$ is $6 \frac{d}{d x} [x]$ .

$e^{6 x} (- \sin (x)) + \cos (x) (e^{6 x} (6 \frac{d}{d x} [x]))$

Step 4.2

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

$e^{6 x} (- \sin (x)) + \cos (x) (e^{6 x} (6 \cdot 1))$

Step 4.3

Simplify the expression.

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Step 4.3.1

Multiply $6$ by $1$ .

$e^{6 x} (- \sin (x)) + \cos (x) (e^{6 x} \cdot 6)$

Step 4.3.2

Move $6$ to the left of $e^{6 x}$ .

$e^{6 x} (- \sin (x)) + \cos (x) (6 \cdot e^{6 x})$

Step 4.3.3

Reorder terms.

$- e^{6 x} \sin (x) + 6 e^{6 x} \cos (x)$