Calculus Examples

$f (x) = x {(4 - x)}^{2}$

Step 1

The function $F (x)$ can be found by finding the indefinite integral of the derivative $f (x)$ .

$F (x) = \int f (x) d x$

Step 2

Set up the integral to solve.

$F (x) = \int x {(4 - x)}^{2} d x$

Step 3

Let $u = 4 - x$ . Then $d u = - d x$ , so $- d u = d x$ . Rewrite using $u$ and $d$ $u$ .

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Step 3.1

Let $u = 4 - x$ . Find $\frac{d u}{d x}$ .

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Step 3.1.1

Differentiate $4 - x$ .

$\frac{d}{d x} [4 - x]$

Step 3.1.2

Differentiate.

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Step 3.1.2.1

By the Sum Rule, the derivative of $4 - x$ with respect to $x$ is $\frac{d}{d x} [4] + \frac{d}{d x} [- x]$ .

$\frac{d}{d x} [4] + \frac{d}{d x} [- x]$

Step 3.1.2.2

Since $4$ is constant with respect to $x$ , the derivative of $4$ with respect to $x$ is $0$ .

$0 + \frac{d}{d x} [- x]$

Step 3.1.3

Evaluate $\frac{d}{d x} [- x]$ .

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Step 3.1.3.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$0 - \frac{d}{d x} [x]$

Step 3.1.3.2

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

$0 - 1 \cdot 1$

Step 3.1.3.3

Multiply $- 1$ by $1$ .

$0 - 1$

Step 3.1.4

Subtract $1$ from $0$ .

$- 1$

Step 3.2

Rewrite the problem using $u$ and $d u$ .

$\int - (- u + 4) u^{2} d u$

Step 4

Expand $- (- u + 4) u^{2}$ .

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Step 4.1

Apply the distributive property.

$\int (- - u - 1 \cdot 4) u^{2} d u$

Step 4.2

Apply the distributive property.

$\int - - u u^{2} - 1 \cdot 4 u^{2} d u$

Step 4.3

Move parentheses.

$\int - - 1 u \cdot u^{2} - 1 \cdot 4 u^{2} d u$

Step 4.4

Multiply $- 1$ by $- 1$ .

$\int 1 u \cdot u^{2} - 1 \cdot 4 u^{2} d u$

Step 4.5

Multiply $u$ by $1$ .

$\int u \cdot u^{2} - 1 \cdot 4 u^{2} d u$

Step 4.6

Raise $u$ to the power of $1$ .

$\int u^{1} u^{2} - 1 \cdot 4 u^{2} d u$

Step 4.7

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$\int u^{1 + 2} - 1 \cdot 4 u^{2} d u$

Step 4.8

Add $1$ and $2$ .

$\int u^{3} - 1 \cdot 4 u^{2} d u$

Step 4.9

Multiply $- 1$ by $4$ .

$\int u^{3} - 4 u^{2} d u$

Step 5

Split the single integral into multiple integrals.

$\int u^{3} d u + \int - 4 u^{2} d u$

Step 6

By the Power Rule, the integral of $u^{3}$ with respect to $u$ is $\frac{1}{4} u^{4}$ .

$\frac{1}{4} u^{4} + C + \int - 4 u^{2} d u$

Step 7

Since $- 4$ is constant with respect to $u$ , move $- 4$ out of the integral.

$\frac{1}{4} u^{4} + C - 4 \int u^{2} d u$

Step 8

By the Power Rule, the integral of $u^{2}$ with respect to $u$ is $\frac{1}{3} u^{3}$ .

$\frac{1}{4} u^{4} + C - 4 (\frac{1}{3} u^{3} + C)$

Step 9

Simplify.

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Step 9.1

Simplify.

$\frac{1}{4} u^{4} - 4 (\frac{1}{3}) u^{3} + C$

Step 9.2

Simplify.

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Step 9.2.1

Combine $- 4$ and $\frac{1}{3}$ .

$\frac{1}{4} u^{4} + \frac{- 4}{3} u^{3} + C$

Step 9.2.2

Move the negative in front of the fraction.

$\frac{1}{4} u^{4} - \frac{4}{3} u^{3} + C$

Step 10

Replace all occurrences of $u$ with $4 - x$ .

$\frac{1}{4} {(4 - x)}^{4} - \frac{4}{3} {(4 - x)}^{3} + C$

Step 11

The answer is the antiderivative of the function $f (x) = x {(4 - x)}^{2}$ .

$F (x) =$ $\frac{1}{4} {(4 - x)}^{4} - \frac{4}{3} {(4 - x)}^{3} + C$