Calculus Examples

$\int \frac{x^{2}}{\sqrt{1 - x^{2}}} d x$

Step 1

Let $x = \sin (t)$ , where $- \frac{π}{2} \leq t \leq \frac{π}{2}$ . Then $d x = \cos (t) d t$ . Note that since $- \frac{π}{2} \leq t \leq \frac{π}{2}$ , $\cos (t)$ is positive.

$\int \frac{\sin^{2} (t)}{\sqrt{1 - \sin^{2} (t)}} \cos (t) d t$

Step 2

Simplify terms.

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Step 2.1

Simplify $\sqrt{1 - \sin^{2} (t)}$ .

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Step 2.1.1

Apply pythagorean identity.

$\int \frac{\sin^{2} (t)}{\sqrt{\cos^{2} (t)}} \cos (t) d t$

Step 2.1.2

Pull terms out from under the radical, assuming positive real numbers.

$\int \frac{\sin^{2} (t)}{\cos (t)} \cos (t) d t$

Step 2.2

Cancel the common factor of $\cos (t)$ .

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Step 2.2.1

Cancel the common factor.

$\int \frac{\sin^{2} (t)}{\cos (t)} \cos (t) d t$

Step 2.2.2

Rewrite the expression.

$\int \sin^{2} (t) d t$

Step 3

Use the half-angle formula to rewrite $\sin^{2} (t)$ as $\frac{1 - \cos (2 t)}{2}$ .

$\int \frac{1 - \cos (2 t)}{2} d t$

Step 4

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

$\frac{1}{2} \int 1 - \cos (2 t) d t$

Step 5

Split the single integral into multiple integrals.

$\frac{1}{2} (\int d t + \int - \cos (2 t) d t)$

Step 6

Apply the constant rule.

$\frac{1}{2} (t + C + \int - \cos (2 t) d t)$

Step 7

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

$\frac{1}{2} (t + C - \int \cos (2 t) d t)$

Step 8

Let $u = 2 t$ . Then $d u = 2 d t$ , so $\frac{1}{2} d u = d t$ . Rewrite using $u$ and $d$ $u$ .

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Step 8.1

Let $u = 2 t$ . Find $\frac{d u}{d t}$ .

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Step 8.1.1

Differentiate $2 t$ .

$\frac{d}{d t} [2 t]$

Step 8.1.2

Since $2$ is constant with respect to $t$ , the derivative of $2 t$ with respect to $t$ is $2 \frac{d}{d t} [t]$ .

$2 \frac{d}{d t} [t]$

Step 8.1.3

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

$2 \cdot 1$

Step 8.1.4

Multiply $2$ by $1$ .

$2$

Step 8.2

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

$\frac{1}{2} (t + C - \int \cos (u) \frac{1}{2} d u)$

Step 9

Combine $\cos (u)$ and $\frac{1}{2}$ .

$\frac{1}{2} (t + C - \int \frac{\cos (u)}{2} d u)$

Step 10

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

$\frac{1}{2} (t + C - (\frac{1}{2} \int \cos (u) d u))$

Step 11

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

$\frac{1}{2} (t + C - \frac{1}{2} (\sin (u) + C))$

Step 12

Simplify.

$\frac{1}{2} (t - \frac{1}{2} \sin (u)) + C$

Step 13

Substitute back in for each integration substitution variable.

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Step 13.1

Replace all occurrences of $t$ with $\arcsin (x)$ .

$\frac{1}{2} (\arcsin (x) - \frac{1}{2} \sin (u)) + C$

Step 13.2

Replace all occurrences of $u$ with $2 t$ .

$\frac{1}{2} (\arcsin (x) - \frac{1}{2} \sin (2 t)) + C$

Step 13.3

Replace all occurrences of $t$ with $\arcsin (x)$ .

$\frac{1}{2} (\arcsin (x) - \frac{1}{2} \sin (2 \arcsin (x))) + C$

Step 14

Simplify.

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Step 14.1

Combine $\sin (2 \arcsin (x))$ and $\frac{1}{2}$ .

$\frac{1}{2} (\arcsin (x) - \frac{\sin (2 \arcsin (x))}{2}) + C$

Step 14.2

Apply the distributive property.

$\frac{1}{2} \arcsin (x) + \frac{1}{2} (- \frac{\sin (2 \arcsin (x))}{2}) + C$

Step 14.3

Combine $\frac{1}{2}$ and $\arcsin (x)$ .

$\frac{\arcsin (x)}{2} + \frac{1}{2} (- \frac{\sin (2 \arcsin (x))}{2}) + C$

Step 14.4

Multiply $\frac{1}{2} (- \frac{\sin (2 \arcsin (x))}{2})$ .

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Step 14.4.1

Multiply $\frac{1}{2}$ by $\frac{\sin (2 \arcsin (x))}{2}$ .

$\frac{\arcsin (x)}{2} - \frac{\sin (2 \arcsin (x))}{2 \cdot 2} + C$

Step 14.4.2

Multiply $2$ by $2$ .

$\frac{\arcsin (x)}{2} - \frac{\sin (2 \arcsin (x))}{4} + C$

Step 15

Reorder terms.

$\frac{1}{2} \arcsin (x) - \frac{1}{4} \sin (2 \arcsin (x)) + C$