Calculus Examples

$(x^{2} + 1) \sin (3 x - 1)$

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 $f (x) = x^{2} + 1$ and $g (x) = \sin (3 x - 1)$ .

$(x^{2} + 1) \frac{d}{d x} [\sin (3 x - 1)] + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = 3 x - 1$ .

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Step 2.1

To apply the Chain Rule, set $u$ as $3 x - 1$ .

$(x^{2} + 1) (\frac{d}{d u} [\sin (u)] \frac{d}{d x} [3 x - 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 2.2

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

$(x^{2} + 1) (\cos (u) \frac{d}{d x} [3 x - 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 2.3

Replace all occurrences of $u$ with $3 x - 1$ .

$(x^{2} + 1) (\cos (3 x - 1) \frac{d}{d x} [3 x - 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3

Differentiate.

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Step 3.1

By the Sum Rule, the derivative of $3 x - 1$ with respect to $x$ is $\frac{d}{d x} [3 x] + \frac{d}{d x} [- 1]$ .

$(x^{2} + 1) \cos (3 x - 1) (\frac{d}{d x} [3 x] + \frac{d}{d x} [- 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.2

Since $3$ is constant with respect to $x$ , the derivative of $3 x$ with respect to $x$ is $3 \frac{d}{d x} [x]$ .

$(x^{2} + 1) \cos (3 x - 1) (3 \frac{d}{d x} [x] + \frac{d}{d x} [- 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.3

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

$(x^{2} + 1) \cos (3 x - 1) (3 \cdot 1 + \frac{d}{d x} [- 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.4

Multiply $3$ by $1$ .

$(x^{2} + 1) \cos (3 x - 1) (3 + \frac{d}{d x} [- 1]) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.5

Since $- 1$ is constant with respect to $x$ , the derivative of $- 1$ with respect to $x$ is $0$ .

$(x^{2} + 1) \cos (3 x - 1) (3 + 0) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.6

Simplify the expression.

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Step 3.6.1

Add $3$ and $0$ .

$(x^{2} + 1) \cos (3 x - 1) \cdot 3 + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.6.2

Move $3$ to the left of $(x^{2} + 1) \cos (3 x - 1)$ .

$3 \cdot ((x^{2} + 1) \cos (3 x - 1)) + \sin (3 x - 1) \frac{d}{d x} [x^{2} + 1]$

Step 3.7

By the Sum Rule, the derivative of $x^{2} + 1$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [1]$ .

$3 (x^{2} + 1) \cos (3 x - 1) + \sin (3 x - 1) (\frac{d}{d x} [x^{2}] + \frac{d}{d x} [1])$

Step 3.8

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$3 (x^{2} + 1) \cos (3 x - 1) + \sin (3 x - 1) (2 x + \frac{d}{d x} [1])$

Step 3.9

Since $1$ is constant with respect to $x$ , the derivative of $1$ with respect to $x$ is $0$ .

$3 (x^{2} + 1) \cos (3 x - 1) + \sin (3 x - 1) (2 x + 0)$

Step 3.10

Add $2 x$ and $0$ .

$3 (x^{2} + 1) \cos (3 x - 1) + \sin (3 x - 1) (2 x)$

Step 4

Simplify.

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Step 4.1

Apply the distributive property.

$(3 x^{2} + 3 \cdot 1) \cos (3 x - 1) + \sin (3 x - 1) (2 x)$

Step 4.2

Multiply $3$ by $1$ .

$(3 x^{2} + 3) \cos (3 x - 1) + \sin (3 x - 1) (2 x)$

Step 4.3

Reorder terms.

$\cos (3 x - 1) (3 x^{2} + 3) + 2 x \sin (3 x - 1)$