Calculus Examples

$\int x \sqrt{4 - x} d x$

Step 1

Integrate by parts using the formula $\int u d v = u v - \int v d u$ , where $u = x$ and $d v = \sqrt{4 - x}$ .

$x (- \frac{2}{3} {(4 - x)}^{\frac{3}{2}}) - \int - \frac{2}{3} {(4 - x)}^{\frac{3}{2}} d x$

Step 2

Simplify.

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Step 2.1

Combine ${(4 - x)}^{\frac{3}{2}}$ and $\frac{2}{3}$ .

$x (- \frac{{(4 - x)}^{\frac{3}{2}} \cdot 2}{3}) - \int - \frac{2}{3} {(4 - x)}^{\frac{3}{2}} d x$

Step 2.2

Combine $x$ and $\frac{{(4 - x)}^{\frac{3}{2}} \cdot 2}{3}$ .

$- \frac{x ({(4 - x)}^{\frac{3}{2}} \cdot 2)}{3} - \int - \frac{2}{3} {(4 - x)}^{\frac{3}{2}} d x$

Step 2.3

Move $2$ to the left of ${(4 - x)}^{\frac{3}{2}}$ .

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} - \int - \frac{2}{3} {(4 - x)}^{\frac{3}{2}} d x$

Step 3

Since $- \frac{2}{3}$ is constant with respect to $x$ , move $- \frac{2}{3}$ out of the integral.

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} - (- \frac{2}{3} \int {(4 - x)}^{\frac{3}{2}} d x)$

Step 4

Simplify.

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Step 4.1

Multiply $- 1$ by $- 1$ .

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + 1 (\frac{2}{3} \int {(4 - x)}^{\frac{3}{2}} d x)$

Step 4.2

Multiply $\frac{2}{3}$ by $1$ .

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + \frac{2}{3} \int {(4 - x)}^{\frac{3}{2}} d x$

Step 5

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 5.1

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

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Step 5.1.1

Differentiate $4 - x$ .

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

Step 5.1.2

Differentiate.

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Step 5.1.2.1

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 5.1.2.2

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 5.1.3

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

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Step 5.1.3.1

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 5.1.3.2

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 5.1.3.3

Multiply $- 1$ by $1$ .

$0 - 1$

Step 5.1.4

Subtract $1$ from $0$ .

$- 1$

Step 5.2

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

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + \frac{2}{3} \int - u^{\frac{3}{2}} d u$

Step 6

Since $- 1$ is constant with respect to $u$ , move $- 1$ out of the integral.

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + \frac{2}{3} (- \int u^{\frac{3}{2}} d u)$

Step 7

By the Power Rule, the integral of $u^{\frac{3}{2}}$ with respect to $u$ is $\frac{2}{5} u^{\frac{5}{2}}$ .

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + \frac{2}{3} (- (\frac{2}{5} u^{\frac{5}{2}} + C))$

Step 8

Simplify.

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Step 8.1

Combine $\frac{2}{5}$ and $u^{\frac{5}{2}}$ .

$- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + \frac{2}{3} (- (\frac{2 u^{\frac{5}{2}}}{5} + C))$

Step 8.2

Rewrite $- \frac{x (2 {(4 - x)}^{\frac{3}{2}})}{3} + \frac{2}{3} (- (\frac{2 u^{\frac{5}{2}}}{5} + C))$ as $- \frac{2}{3} x {(4 - x)}^{\frac{3}{2}} + \frac{2}{3} (- \frac{2}{5} u^{\frac{5}{2}}) + C$ .

$- \frac{2}{3} x {(4 - x)}^{\frac{3}{2}} + \frac{2}{3} (- \frac{2}{5} u^{\frac{5}{2}}) + C$

Step 8.3

Simplify.

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Step 8.3.1

Combine $x$ and $\frac{2}{3}$ .

$- \frac{x \cdot 2}{3} {(4 - x)}^{\frac{3}{2}} + \frac{2}{3} (- \frac{2}{5} u^{\frac{5}{2}}) + C$

Step 8.3.2

Combine ${(4 - x)}^{\frac{3}{2}}$ and $\frac{x \cdot 2}{3}$ .

$- \frac{{(4 - x)}^{\frac{3}{2}} (x \cdot 2)}{3} + \frac{2}{3} (- \frac{2}{5} u^{\frac{5}{2}}) + C$

Step 8.3.3

Move $2$ to the left of $x$ .

$- \frac{{(4 - x)}^{\frac{3}{2}} (2 \cdot x)}{3} + \frac{2}{3} (- \frac{2}{5} u^{\frac{5}{2}}) + C$

Step 8.3.4

Move $2$ to the left of ${(4 - x)}^{\frac{3}{2}}$ .

$- \frac{2 \cdot {(4 - x)}^{\frac{3}{2}} x}{3} + \frac{2}{3} (- \frac{2}{5} u^{\frac{5}{2}}) + C$

Step 8.3.5

Combine $u^{\frac{5}{2}}$ and $\frac{2}{5}$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x}{3} + \frac{2}{3} (- \frac{u^{\frac{5}{2}} \cdot 2}{5}) + C$

Step 8.3.6

Multiply $\frac{2}{3}$ by $\frac{u^{\frac{5}{2}} \cdot 2}{5}$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x}{3} - \frac{2 (u^{\frac{5}{2}} \cdot 2)}{3 \cdot 5} + C$

Step 8.3.7

Multiply $2$ by $2$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x}{3} - \frac{4 u^{\frac{5}{2}}}{3 \cdot 5} + C$

Step 8.3.8

Multiply $3$ by $5$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x}{3} - \frac{4 u^{\frac{5}{2}}}{15} + C$

Step 8.3.9

To write $- \frac{2 {(4 - x)}^{\frac{3}{2}} x}{3}$ as a fraction with a common denominator, multiply by $\frac{5}{5}$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x}{3} \cdot \frac{5}{5} - \frac{4 u^{\frac{5}{2}}}{15} + C$

Step 8.3.10

Write each expression with a common denominator of $15$ , by multiplying each by an appropriate factor of $1$ .

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Step 8.3.10.1

Multiply $\frac{2 {(4 - x)}^{\frac{3}{2}} x}{3}$ by $\frac{5}{5}$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x \cdot 5}{3 \cdot 5} - \frac{4 u^{\frac{5}{2}}}{15} + C$

Step 8.3.10.2

Multiply $3$ by $5$ .

$- \frac{2 {(4 - x)}^{\frac{3}{2}} x \cdot 5}{15} - \frac{4 u^{\frac{5}{2}}}{15} + C$

Step 8.3.11

Combine the numerators over the common denominator.

$\frac{- 2 {(4 - x)}^{\frac{3}{2}} x \cdot 5 - 4 u^{\frac{5}{2}}}{15} + C$

Step 8.3.12

Multiply $5$ by $- 2$ .

$\frac{- 10 {(4 - x)}^{\frac{3}{2}} x - 4 u^{\frac{5}{2}}}{15} + C$

Step 9

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

$\frac{- 10 {(4 - x)}^{\frac{3}{2}} x - 4 {(4 - x)}^{\frac{5}{2}}}{15} + C$

Step 10

Reorder terms.

$\frac{1}{15} (- 10 {(4 - x)}^{\frac{3}{2}} x - 4 {(4 - x)}^{\frac{5}{2}}) + C$