Calculus Examples

$\frac{d y}{d x} = \frac{2 x}{x^{2} - 9}$

Step 1

Rewrite the equation.

$d y = \frac{2 x}{x^{2} - 9} d x$

Step 2

Integrate both sides.

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Step 2.1

Set up an integral on each side.

$\int d y = \int \frac{2 x}{x^{2} - 9} d x$

Step 2.2

Apply the constant rule.

$y + C_{1} = \int \frac{2 x}{x^{2} - 9} d x$

Step 2.3

Integrate the right side.

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Step 2.3.1

Since $2$ is constant with respect to $x$ , move $2$ out of the integral.

$y + C_{1} = 2 \int \frac{x}{x^{2} - 9} d x$

Step 2.3.2

Let $u = x^{2} - 9$ . Then $d u = 2 x d x$ , so $\frac{1}{2} d u = x d x$ . Rewrite using $u$ and $d$ $u$ .

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Step 2.3.2.1

Let $u = x^{2} - 9$ . Find $\frac{d u}{d x}$ .

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Step 2.3.2.1.1

Differentiate $x^{2} - 9$ .

$\frac{d}{d x} [x^{2} - 9]$

Step 2.3.2.1.2

By the Sum Rule, the derivative of $x^{2} - 9$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 9]$ .

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

Step 2.3.2.1.3

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

$2 x + \frac{d}{d x} [- 9]$

Step 2.3.2.1.4

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

$2 x + 0$

Step 2.3.2.1.5

Add $2 x$ and $0$ .

$2 x$

Step 2.3.2.2

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

$y + C_{1} = 2 \int \frac{1}{u} \cdot \frac{1}{2} d u$

Step 2.3.3

Simplify.

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Step 2.3.3.1

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

$y + C_{1} = 2 \int \frac{1}{u \cdot 2} d u$

Step 2.3.3.2

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

$y + C_{1} = 2 \int \frac{1}{2 u} d u$

Step 2.3.4

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

$y + C_{1} = 2 (\frac{1}{2} \int \frac{1}{u} d u)$

Step 2.3.5

Simplify.

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Step 2.3.5.1

Combine $\frac{1}{2}$ and $2$ .

$y + C_{1} = \frac{2}{2} \int \frac{1}{u} d u$

Step 2.3.5.2

Cancel the common factor of $2$ .

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Step 2.3.5.2.1

Cancel the common factor.

$y + C_{1} = \frac{2}{2} \int \frac{1}{u} d u$

Step 2.3.5.2.2

Rewrite the expression.

$y + C_{1} = 1 \int \frac{1}{u} d u$

Step 2.3.5.3

Multiply $\int \frac{1}{u} d u$ by $1$ .

$y + C_{1} = \int \frac{1}{u} d u$

Step 2.3.6

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

$y + C_{1} = \ln (| u |) + C_{2}$

Step 2.3.7

Replace all occurrences of $u$ with $x^{2} - 9$ .

$y + C_{1} = \ln (| x^{2} - 9 |) + C_{2}$

Step 2.4

Group the constant of integration on the right side as $C$ .

$y = \ln (| x^{2} - 9 |) + C$