Calculus Examples

$s = \sin (\frac{9 π t}{2}) - \cos (\frac{9 π t}{2})$

Step 1

Differentiate both sides of the equation.

$\frac{d}{d t} (s) = \frac{d}{d t} (\sin (\frac{9 π t}{2}) - \cos (\frac{9 π t}{2}))$

Step 2

The derivative of $s$ with respect to $t$ is $s'$ .

$s'$

Step 3

Differentiate the right side of the equation.

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Step 3.1

By the Sum Rule, the derivative of $\sin (\frac{9 π t}{2}) - \cos (\frac{9 π t}{2})$ with respect to $t$ is $\frac{d}{d t} [\sin (\frac{9 π t}{2})] + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$ .

$\frac{d}{d t} [\sin (\frac{9 π t}{2})] + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2

Evaluate $\frac{d}{d t} [\sin (\frac{9 π t}{2})]$ .

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Step 3.2.1

Differentiate using the chain rule, which states that $\frac{d}{d t} [f (g (t))]$ is $f' (g (t)) g' (t)$ where $f (t) = \sin (t)$ and $g (t) = \frac{9 π t}{2}$ .

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Step 3.2.1.1

To apply the Chain Rule, set $u_{1}$ as $\frac{9 π t}{2}$ .

$\frac{d}{d u_{1}} [\sin (u_{1})] \frac{d}{d t} [\frac{9 π t}{2}] + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.1.2

The derivative of $\sin (u_{1})$ with respect to $u_{1}$ is $\cos (u_{1})$ .

$\cos (u_{1}) \frac{d}{d t} [\frac{9 π t}{2}] + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.1.3

Replace all occurrences of $u_{1}$ with $\frac{9 π t}{2}$ .

$\cos (\frac{9 π t}{2}) \frac{d}{d t} [\frac{9 π t}{2}] + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.2

Since $\frac{9 π}{2}$ is constant with respect to $t$ , the derivative of $\frac{9 π t}{2}$ with respect to $t$ is $\frac{9 π}{2} \frac{d}{d t} [t]$ .

$\cos (\frac{9 π t}{2}) (\frac{9 π}{2} \frac{d}{d t} [t]) + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.3

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

$\cos (\frac{9 π t}{2}) (\frac{9 π}{2} \cdot 1) + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.4

Multiply $\frac{9 π}{2}$ by $1$ .

$\cos (\frac{9 π t}{2}) \frac{9 π}{2} + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.5

Combine $\cos (\frac{9 π t}{2})$ and $\frac{9 π}{2}$ .

$\frac{\cos (\frac{9 π t}{2}) (9 π)}{2} + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.2.6

Move $9$ to the left of $\cos (\frac{9 π t}{2})$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} + \frac{d}{d t} [- \cos (\frac{9 π t}{2})]$

Step 3.3

Evaluate $\frac{d}{d t} [- \cos (\frac{9 π t}{2})]$ .

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Step 3.3.1

Since $- 1$ is constant with respect to $t$ , the derivative of $- \cos (\frac{9 π t}{2})$ with respect to $t$ is $- \frac{d}{d t} [\cos (\frac{9 π t}{2})]$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - \frac{d}{d t} [\cos (\frac{9 π t}{2})]$

Step 3.3.2

Differentiate using the chain rule, which states that $\frac{d}{d t} [f (g (t))]$ is $f' (g (t)) g' (t)$ where $f (t) = \cos (t)$ and $g (t) = \frac{9 π t}{2}$ .

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Step 3.3.2.1

To apply the Chain Rule, set $u_{2}$ as $\frac{9 π t}{2}$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - (\frac{d}{d u_{2}} [\cos (u_{2})] \frac{d}{d t} [\frac{9 π t}{2}])$

Step 3.3.2.2

The derivative of $\cos (u_{2})$ with respect to $u_{2}$ is $- \sin (u_{2})$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - (- \sin (u_{2}) \frac{d}{d t} [\frac{9 π t}{2}])$

Step 3.3.2.3

Replace all occurrences of $u_{2}$ with $\frac{9 π t}{2}$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - (- \sin (\frac{9 π t}{2}) \frac{d}{d t} [\frac{9 π t}{2}])$

Step 3.3.3

Since $\frac{9 π}{2}$ is constant with respect to $t$ , the derivative of $\frac{9 π t}{2}$ with respect to $t$ is $\frac{9 π}{2} \frac{d}{d t} [t]$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - (- \sin (\frac{9 π t}{2}) (\frac{9 π}{2} \frac{d}{d t} [t]))$

Step 3.3.4

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

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - (- \sin (\frac{9 π t}{2}) (\frac{9 π}{2} \cdot 1))$

Step 3.3.5

Multiply $\frac{9 π}{2}$ by $1$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - (- \sin (\frac{9 π t}{2}) \frac{9 π}{2})$

Step 3.3.6

Combine $\frac{9 π}{2}$ and $\sin (\frac{9 π t}{2})$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} - - \frac{9 π \sin (\frac{9 π t}{2})}{2}$

Step 3.3.7

Multiply $- 1$ by $- 1$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} + 1 \frac{9 π \sin (\frac{9 π t}{2})}{2}$

Step 3.3.8

Multiply $\frac{9 π \sin (\frac{9 π t}{2})}{2}$ by $1$ .

$\frac{9 \cos (\frac{9 π t}{2}) π}{2} + \frac{9 π \sin (\frac{9 π t}{2})}{2}$

Step 3.4

Reorder factors in $\frac{9 \cos (\frac{9 π t}{2}) π}{2} + \frac{9 π \sin (\frac{9 π t}{2})}{2}$ .

$\frac{9 π \cos (\frac{9 π t}{2})}{2} + \frac{9 π \sin (\frac{9 π t}{2})}{2}$

Step 4

Reform the equation by setting the left side equal to the right side.

$s' = \frac{9 π \cos (\frac{9 π t}{2})}{2} + \frac{9 π \sin (\frac{9 π t}{2})}{2}$

Step 5

Replace $s'$ with $\frac{d s}{d t}$ .

$\frac{d s}{d t} = \frac{9 π \cos (\frac{9 π t}{2})}{2} + \frac{9 π \sin (\frac{9 π t}{2})}{2}$