Calculus Examples

$f (x) = x {(3 x - 9)}^{3}$

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 $f (x) = x$ and $g (x) = {(3 x - 9)}^{3}$ .

$x \frac{d}{d x} [{(3 x - 9)}^{3}] + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{3}$ and $g (x) = 3 x - 9$ .

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Step 2.1

To apply the Chain Rule, set $u$ as $3 x - 9$ .

$x (\frac{d}{d u} [u^{3}] \frac{d}{d x} [3 x - 9]) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 2.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 3$ .

$x (3 u^{2} \frac{d}{d x} [3 x - 9]) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 2.3

Replace all occurrences of $u$ with $3 x - 9$ .

$x (3 {(3 x - 9)}^{2} \frac{d}{d x} [3 x - 9]) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3

Differentiate.

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Step 3.1

By the Sum Rule, the derivative of $3 x - 9$ with respect to $x$ is $\frac{d}{d x} [3 x] + \frac{d}{d x} [- 9]$ .

$x (3 {(3 x - 9)}^{2} (\frac{d}{d x} [3 x] + \frac{d}{d x} [- 9])) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.2

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

$x (3 {(3 x - 9)}^{2} (3 \frac{d}{d x} [x] + \frac{d}{d x} [- 9])) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.3

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

$x (3 {(3 x - 9)}^{2} (3 \cdot 1 + \frac{d}{d x} [- 9])) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.4

Multiply $3$ by $1$ .

$x (3 {(3 x - 9)}^{2} (3 + \frac{d}{d x} [- 9])) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.5

Since $- 9$ is constant with respect to $x$ , the derivative of $- 9$ with respect to $x$ is $0$ .

$x (3 {(3 x - 9)}^{2} (3 + 0)) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.6

Simplify the expression.

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Step 3.6.1

Add $3$ and $0$ .

$x (3 {(3 x - 9)}^{2} \cdot 3) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.6.2

Multiply $3$ by $3$ .

$x (9 {(3 x - 9)}^{2}) + {(3 x - 9)}^{3} \frac{d}{d x} [x]$

Step 3.7

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

$x (9 {(3 x - 9)}^{2}) + {(3 x - 9)}^{3} \cdot 1$

Step 3.8

Multiply ${(3 x - 9)}^{3}$ by $1$ .

$x (9 {(3 x - 9)}^{2}) + {(3 x - 9)}^{3}$

Step 4

Simplify.

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Step 4.1

Factor ${(3 x - 9)}^{2}$ out of $x (9 {(3 x - 9)}^{2}) + {(3 x - 9)}^{3}$ .

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Step 4.1.1

Factor ${(3 x - 9)}^{2}$ out of $x (9 {(3 x - 9)}^{2})$ .

${(3 x - 9)}^{2} (x \cdot (9)) + {(3 x - 9)}^{3}$

Step 4.1.2

Factor ${(3 x - 9)}^{2}$ out of ${(3 x - 9)}^{3}$ .

${(3 x - 9)}^{2} (x \cdot (9)) + {(3 x - 9)}^{2} (3 x - 9)$

Step 4.1.3

Factor ${(3 x - 9)}^{2}$ out of ${(3 x - 9)}^{2} (x \cdot (9)) + {(3 x - 9)}^{2} (3 x - 9)$ .

${(3 x - 9)}^{2} (x \cdot (9) + 3 x - 9)$

Step 4.2

Combine terms.

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Step 4.2.1

Move $9$ to the left of $x$ .

${(3 x - 9)}^{2} (9 \cdot x + 3 x - 9)$

Step 4.2.2

Add $9 x$ and $3 x$ .

${(3 x - 9)}^{2} (12 x - 9)$