Calculus Examples

$y = {\cos (9 x)}^{x}$

Step 1

Use the properties of logarithms to simplify the differentiation.

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Step 1.1

Rewrite ${\cos (9 x)}^{x}$ as $e^{\ln ({\cos (9 x)}^{x})}$ .

$\frac{d}{d x} [e^{\ln ({\cos (9 x)}^{x})}]$

Step 1.2

Expand $\ln ({\cos (9 x)}^{x})$ by moving $x$ outside the logarithm.

$\frac{d}{d x} [e^{x \ln (\cos (9 x))}]$

Step 2

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 $g (x) = x \ln (\cos (9 x))$ .

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Step 2.1

To apply the Chain Rule, set $u_{1}$ as $x \ln (\cos (9 x))$ .

$\frac{d}{d u_{1}} [e^{u_{1}}] \frac{d}{d x} [x \ln (\cos (9 x))]$

Step 2.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{1}} [a^{u_{1}}]$ is $a^{u_{1}} \ln (a)$ where $a$ = $e$ .

$e^{u_{1}} \frac{d}{d x} [x \ln (\cos (9 x))]$

Step 2.3

Replace all occurrences of $u_{1}$ with $x \ln (\cos (9 x))$ .

$e^{x \ln (\cos (9 x))} \frac{d}{d x} [x \ln (\cos (9 x))]$

Step 3

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 $f (x) = x$ and $g (x) = \ln (\cos (9 x))$ .

$e^{x \ln (\cos (9 x))} (x \frac{d}{d x} [\ln (\cos (9 x))] + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 4

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 $g (x) = \cos (9 x)$ .

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Step 4.1

To apply the Chain Rule, set $u_{2}$ as $\cos (9 x)$ .

$e^{x \ln (\cos (9 x))} (x (\frac{d}{d u_{2}} [\ln (u_{2})] \frac{d}{d x} [\cos (9 x)]) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 4.2

The derivative of $\ln (u_{2})$ with respect to $u_{2}$ is $\frac{1}{u_{2}}$ .

$e^{x \ln (\cos (9 x))} (x (\frac{1}{u_{2}} \frac{d}{d x} [\cos (9 x)]) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 4.3

Replace all occurrences of $u_{2}$ with $\cos (9 x)$ .

$e^{x \ln (\cos (9 x))} (x (\frac{1}{\cos (9 x)} \frac{d}{d x} [\cos (9 x)]) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 5

Convert from $\frac{1}{\cos (9 x)}$ to $\sec (9 x)$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) \frac{d}{d x} [\cos (9 x)]) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 6

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \cos (x)$ and $g (x) = 9 x$ .

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Step 6.1

To apply the Chain Rule, set $u_{3}$ as $9 x$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (\frac{d}{d u_{3}} [\cos (u_{3})] \frac{d}{d x} [9 x])) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 6.2

The derivative of $\cos (u_{3})$ with respect to $u_{3}$ is $- \sin (u_{3})$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- \sin (u_{3}) \frac{d}{d x} [9 x])) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 6.3

Replace all occurrences of $u_{3}$ with $9 x$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- \sin (9 x) \frac{d}{d x} [9 x])) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 7

Differentiate.

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Step 7.1

Since $9$ is constant with respect to $x$ , the derivative of $9 x$ with respect to $x$ is $9 \frac{d}{d x} [x]$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- \sin (9 x) (9 \frac{d}{d x} [x]))) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 7.2

Multiply $9$ by $- 1$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- 9 \sin (9 x) \frac{d}{d x} [x])) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 7.3

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

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- 9 \sin (9 x) \cdot 1)) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 7.4

Multiply $- 9$ by $1$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- 9 \sin (9 x))) + \ln (\cos (9 x)) \frac{d}{d x} [x])$

Step 7.5

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

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- 9 \sin (9 x))) + \ln (\cos (9 x)) \cdot 1)$

Step 7.6

Multiply $\ln (\cos (9 x))$ by $1$ .

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- 9 \sin (9 x))) + \ln (\cos (9 x)))$

Step 8

Simplify.

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Step 8.1

Apply the distributive property.

$e^{x \ln (\cos (9 x))} (x (\sec (9 x) (- 9 \sin (9 x)))) + e^{x \ln (\cos (9 x))} \ln (\cos (9 x))$

Step 8.2

Remove parentheses.

$e^{x \ln (\cos (9 x))} x \sec (9 x) (- 9 \sin (9 x)) + e^{x \ln (\cos (9 x))} \ln (\cos (9 x))$

Step 8.3

Reorder terms.

$- 9 e^{x \ln (\cos (9 x))} x \sec (9 x) \sin (9 x) + e^{x \ln (\cos (9 x))} \ln (\cos (9 x))$