Calculus Examples

$(\int x^{2} \ln (x^{2} + 1) d x)$

Step 1

Let $u_{1} = x^{2} + 1$ . Then $d u_{1} = 2 x d x$ , so $\frac{1}{2} d u_{1} = x d x$ . Rewrite using $u_{1}$ and $d$ $u_{1}$ .

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Step 1.1

Let $u_{1} = x^{2} + 1$ . Find $\frac{d u_{1}}{d x}$ .

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Step 1.1.1

Differentiate $x^{2} + 1$ .

$\frac{d}{d x} [x^{2} + 1]$

Step 1.1.2

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

$\frac{d}{d x} [x^{2}] + \frac{d}{d x} [1]$

Step 1.1.3

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

$2 x + \frac{d}{d x} [1]$

Step 1.1.4

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

$2 x + 0$

Step 1.1.5

Add $2 x$ and $0$ .

$2 x$

Step 1.2

Rewrite the problem using $u_{1}$ and $d u_{1}$ .

$\int \sqrt{u_{1} - 1} \ln (u_{1}) \frac{1}{2} d u_{1}$

Step 2

Simplify.

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Step 2.1

Combine $\frac{1}{2}$ and $\sqrt{u_{1} - 1}$ .

$\int \frac{\sqrt{u_{1} - 1}}{2} \ln (u_{1}) d u_{1}$

Step 2.2

Combine $\frac{\sqrt{u_{1} - 1}}{2}$ and $\ln (u_{1})$ .

$\int \frac{\sqrt{u_{1} - 1} \ln (u_{1})}{2} d u_{1}$

Step 3

Since $\frac{1}{2}$ is constant with respect to $u_{1}$ , move $\frac{1}{2}$ out of the integral.

$\frac{1}{2} \int \sqrt{u_{1} - 1} \ln (u_{1}) d u_{1}$

Step 4

Integrate by parts using the formula $\int u d v = u v - \int v d u$ , where $u = \ln (u_{1})$ and $d v = \sqrt{u_{1} - 1}$ .

$\frac{1}{2} (\ln (u_{1}) (\frac{2}{3} {u_{2}}^{\frac{3}{2}}) - \int \frac{2}{3} {u_{2}}^{\frac{3}{2}} \frac{1}{u_{1}} d u_{1})$

Step 5

Simplify.

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Step 5.1

Combine $\frac{2}{3}$ and ${u_{2}}^{\frac{3}{2}}$ .

$\frac{1}{2} (\ln (u_{1}) \frac{2 {u_{2}}^{\frac{3}{2}}}{3} - \int \frac{2}{3} {u_{2}}^{\frac{3}{2}} \frac{1}{u_{1}} d u_{1})$

Step 5.2

Combine $\ln (u_{1})$ and $\frac{2 {u_{2}}^{\frac{3}{2}}}{3}$ .

$\frac{1}{2} (\frac{\ln (u_{1}) (2 {u_{2}}^{\frac{3}{2}})}{3} - \int \frac{2}{3} {u_{2}}^{\frac{3}{2}} \frac{1}{u_{1}} d u_{1})$

Step 5.3

Move $2$ to the left of $\ln (u_{1})$ .

$\frac{1}{2} (\frac{2 \cdot \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \int \frac{2}{3} {u_{2}}^{\frac{3}{2}} \frac{1}{u_{1}} d u_{1})$

Step 5.4

Combine $\frac{2}{3}$ and ${u_{2}}^{\frac{3}{2}}$ .

$\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \int \frac{2 {u_{2}}^{\frac{3}{2}}}{3} \cdot \frac{1}{u_{1}} d u_{1})$

Step 5.5

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

$\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \int \frac{2 {u_{2}}^{\frac{3}{2}}}{3 u_{1}} d u_{1})$

Step 6

Since $\frac{2 {u_{2}}^{\frac{3}{2}}}{3}$ is constant with respect to $u_{1}$ , move $\frac{2 {u_{2}}^{\frac{3}{2}}}{3}$ out of the integral.

$\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - (\frac{2 {u_{2}}^{\frac{3}{2}}}{3} \int \frac{1}{u_{1}} d u_{1}))$

Step 7

The integral of $\frac{1}{u_{1}}$ with respect to $u_{1}$ is $\ln (| u_{1} |)$ .

$\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 {u_{2}}^{\frac{3}{2}}}{3} (\ln (| u_{1} |) + C))$

Step 8

Rewrite $\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 {u_{2}}^{\frac{3}{2}}}{3} (\ln (| u_{1} |) + C))$ as $\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 \ln (| u_{1} |) {u_{2}}^{\frac{3}{2}}}{3}) + C$ .

$\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 \ln (| u_{1} |) {u_{2}}^{\frac{3}{2}}}{3}) + C$

Step 9

Remove parentheses.

$\frac{1}{2} (\frac{2}{3} \ln (u_{1}) {u_{2}}^{\frac{3}{2}} - \frac{2}{3} \ln (| u_{1} |) {u_{2}}^{\frac{3}{2}}) + C$

Step 10

Rewrite $\frac{1}{2} (\frac{2}{3} \ln (u_{1}) {u_{2}}^{\frac{3}{2}} - \frac{2}{3} \ln (| u_{1} |) {u_{2}}^{\frac{3}{2}}) + C$ as $\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 {u_{2}}^{\frac{3}{2}} \ln (| u_{1} |)}{3}) + C$ .

$\frac{1}{2} (\frac{2 \ln (u_{1}) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 {u_{2}}^{\frac{3}{2}} \ln (| u_{1} |)}{3}) + C$

Step 11

Substitute back in for each integration substitution variable.

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Step 11.1

Replace all occurrences of $u_{1}$ with $x^{2} + 1$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {u_{2}}^{\frac{3}{2}}}{3} - \frac{2 {u_{2}}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 11.2

Replace all occurrences of $u_{2}$ with $u_{1} - 1$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {(u_{1} - 1)}^{\frac{3}{2}}}{3} - \frac{2 {(u_{1} - 1)}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 11.3

Replace all occurrences of $u_{1}$ with $x^{2} + 1$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {(x^{2} + 1 - 1)}^{\frac{3}{2}}}{3} - \frac{2 {(x^{2} + 1 - 1)}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 12

Simplify.

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Step 12.1

Combine the opposite terms in $\frac{2 \ln (x^{2} + 1) {(x^{2} + 1 - 1)}^{\frac{3}{2}}}{3} - \frac{2 {(x^{2} + 1 - 1)}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}$ .

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Step 12.1.1

Subtract $1$ from $1$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {(x^{2} + 0)}^{\frac{3}{2}}}{3} - \frac{2 {(x^{2} + 1 - 1)}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 12.1.2

Add $x^{2}$ and $0$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {(x^{2})}^{\frac{3}{2}}}{3} - \frac{2 {(x^{2} + 1 - 1)}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 12.1.3

Subtract $1$ from $1$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {(x^{2})}^{\frac{3}{2}}}{3} - \frac{2 {(x^{2} + 0)}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 12.1.4

Add $x^{2}$ and $0$ .

$\frac{1}{2} (\frac{2 \ln (x^{2} + 1) {(x^{2})}^{\frac{3}{2}}}{3} - \frac{2 {(x^{2})}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3}) + C$

Step 12.2

Combine the numerators over the common denominator.

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) {(x^{2})}^{\frac{3}{2}} - 2 {(x^{2})}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3

Simplify the numerator.

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Step 12.3.1

Simplify each term.

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Step 12.3.1.1

Multiply the exponents in ${(x^{2})}^{\frac{3}{2}}$ .

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Step 12.3.1.1.1

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) x^{2 (\frac{3}{2})} - 2 {(x^{2})}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3.1.1.2

Cancel the common factor of $2$ .

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Step 12.3.1.1.2.1

Cancel the common factor.

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) x^{2 (\frac{3}{2})} - 2 {(x^{2})}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3.1.1.2.2

Rewrite the expression.

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) x^{3} - 2 {(x^{2})}^{\frac{3}{2}} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3.1.2

Multiply the exponents in ${(x^{2})}^{\frac{3}{2}}$ .

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Step 12.3.1.2.1

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) x^{3} - 2 x^{2 (\frac{3}{2})} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3.1.2.2

Cancel the common factor of $2$ .

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Step 12.3.1.2.2.1

Cancel the common factor.

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) x^{3} - 2 x^{2 (\frac{3}{2})} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3.1.2.2.2

Rewrite the expression.

$\frac{1}{2} \cdot \frac{2 \ln (x^{2} + 1) x^{3} - 2 x^{3} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.3.2

Reorder factors in $2 \ln (x^{2} + 1) x^{3} - 2 x^{3} \ln (| x^{2} + 1 |)$ .

$\frac{1}{2} \cdot \frac{2 x^{3} \ln (x^{2} + 1) - 2 x^{3} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.4

Simplify the numerator.

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Step 12.4.1

Factor $2 x^{3}$ out of $2 x^{3} \ln (x^{2} + 1) - 2 x^{3} \ln (| x^{2} + 1 |)$ .

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Step 12.4.1.1

Factor $2 x^{3}$ out of $2 x^{3} \ln (x^{2} + 1)$ .

$\frac{1}{2} \cdot \frac{2 x^{3} (\ln (x^{2} + 1)) - 2 x^{3} \ln (| x^{2} + 1 |)}{3} + C$

Step 12.4.1.2

Factor $2 x^{3}$ out of $- 2 x^{3} \ln (| x^{2} + 1 |)$ .

$\frac{1}{2} \cdot \frac{2 x^{3} (\ln (x^{2} + 1)) + 2 x^{3} (- 1 \ln (| x^{2} + 1 |))}{3} + C$

Step 12.4.1.3

Factor $2 x^{3}$ out of $2 x^{3} (\ln (x^{2} + 1)) + 2 x^{3} (- 1 \ln (| x^{2} + 1 |))$ .

$\frac{1}{2} \cdot \frac{2 x^{3} (\ln (x^{2} + 1) - 1 \ln (| x^{2} + 1 |))}{3} + C$

Step 12.4.2

Rewrite $- 1 \ln (| x^{2} + 1 |)$ as $- \ln (| x^{2} + 1 |)$ .

$\frac{1}{2} \cdot \frac{2 x^{3} (\ln (x^{2} + 1) - \ln (| x^{2} + 1 |))}{3} + C$

Step 12.4.3

Use the quotient property of logarithms, $\log_{b} (x) - \log_{b} (y) = \log_{b} (\frac{x}{y})$ .

$\frac{1}{2} \cdot \frac{2 x^{3} \ln (\frac{x^{2} + 1}{| x^{2} + 1 |})}{3} + C$

Step 12.5

Combine.

$\frac{1 (2 x^{3} \ln (\frac{x^{2} + 1}{| x^{2} + 1 |}))}{2 \cdot 3} + C$

Step 12.6

Cancel the common factor of $2$ .

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Step 12.6.1

Cancel the common factor.

$\frac{1 (2 x^{3} \ln (\frac{x^{2} + 1}{| x^{2} + 1 |}))}{2 \cdot 3} + C$

Step 12.6.2

Rewrite the expression.

$\frac{1 (x^{3} \ln (\frac{x^{2} + 1}{| x^{2} + 1 |}))}{3} + C$

Step 12.7

Multiply $x^{3}$ by $1$ .

$\frac{x^{3} \ln (\frac{x^{2} + 1}{| x^{2} + 1 |})}{3} + C$

$\frac{1}{3} x^{3} \ln (\frac{x^{2} + 1}{| x^{2} + 1 |}) + C$