Calculus Examples

$7 x - 8 y \sqrt{x^{2} + 1} \frac{d y}{d x} = 0$

Step 1

Separate the variables.

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Step 1.1

Solve for $\frac{d y}{d x}$ .

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Step 1.1.1

Subtract $7 x$ from both sides of the equation.

$- 8 y \sqrt{x^{2} + 1} \frac{d y}{d x} = - 7 x$

Step 1.1.2

Divide each term in $- 8 y \sqrt{x^{2} + 1} \frac{d y}{d x} = - 7 x$ by $- 8 y \sqrt{x^{2} + 1}$ and simplify.

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Step 1.1.2.1

Divide each term in $- 8 y \sqrt{x^{2} + 1} \frac{d y}{d x} = - 7 x$ by $- 8 y \sqrt{x^{2} + 1}$ .

$\frac{- 8 y \sqrt{x^{2} + 1} \frac{d y}{d x}}{- 8 y \sqrt{x^{2} + 1}} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.2

Simplify the left side.

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Step 1.1.2.2.1

Cancel the common factor of $- 8$ .

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Step 1.1.2.2.1.1

Cancel the common factor.

$\frac{- 8 y \sqrt{x^{2} + 1} \frac{d y}{d x}}{- 8 y \sqrt{x^{2} + 1}} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.2.1.2

Rewrite the expression.

$\frac{y \sqrt{x^{2} + 1} \frac{d y}{d x}}{y \sqrt{x^{2} + 1}} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.2.2

Cancel the common factor of $y$ .

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Step 1.1.2.2.2.1

Cancel the common factor.

$\frac{y \sqrt{x^{2} + 1} \frac{d y}{d x}}{y \sqrt{x^{2} + 1}} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.2.2.2

Rewrite the expression.

$\frac{\sqrt{x^{2} + 1} \frac{d y}{d x}}{\sqrt{x^{2} + 1}} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.2.3

Cancel the common factor of $\sqrt{x^{2} + 1}$ .

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Step 1.1.2.2.3.1

Cancel the common factor.

$\frac{\sqrt{x^{2} + 1} \frac{d y}{d x}}{\sqrt{x^{2} + 1}} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.2.3.2

Divide $\frac{d y}{d x}$ by $1$ .

$\frac{d y}{d x} = \frac{- 7 x}{- 8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.3

Simplify the right side.

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Step 1.1.2.3.1

Dividing two negative values results in a positive value.

$\frac{d y}{d x} = \frac{7 x}{8 y \sqrt{x^{2} + 1}}$

Step 1.1.2.3.2

Multiply $\frac{7 x}{8 y \sqrt{x^{2} + 1}}$ by $\frac{\sqrt{x^{2} + 1}}{\sqrt{x^{2} + 1}}$ .

$\frac{d y}{d x} = \frac{7 x}{8 y \sqrt{x^{2} + 1}} \cdot \frac{\sqrt{x^{2} + 1}}{\sqrt{x^{2} + 1}}$

Step 1.1.2.3.3

Combine and simplify the denominator.

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Step 1.1.2.3.3.1

Multiply $\frac{7 x}{8 y \sqrt{x^{2} + 1}}$ by $\frac{\sqrt{x^{2} + 1}}{\sqrt{x^{2} + 1}}$ .

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y \sqrt{x^{2} + 1} \sqrt{x^{2} + 1}}$

Step 1.1.2.3.3.2

Move $\sqrt{x^{2} + 1}$ .

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y (\sqrt{x^{2} + 1} \sqrt{x^{2} + 1})}$

Step 1.1.2.3.3.3

Raise $\sqrt{x^{2} + 1}$ to the power of $1$ .

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y ({\sqrt{x^{2} + 1}}^{1} \sqrt{x^{2} + 1})}$

Step 1.1.2.3.3.4

Raise $\sqrt{x^{2} + 1}$ to the power of $1$ .

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y ({\sqrt{x^{2} + 1}}^{1} {\sqrt{x^{2} + 1}}^{1})}$

Step 1.1.2.3.3.5

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

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {\sqrt{x^{2} + 1}}^{1 + 1}}$

Step 1.1.2.3.3.6

Add $1$ and $1$ .

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {\sqrt{x^{2} + 1}}^{2}}$

Step 1.1.2.3.3.7

Rewrite ${\sqrt{x^{2} + 1}}^{2}$ as $x^{2} + 1$ .

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Step 1.1.2.3.3.7.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{x^{2} + 1}$ as ${(x^{2} + 1)}^{\frac{1}{2}}$ .

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {({(x^{2} + 1)}^{\frac{1}{2}})}^{2}}$

Step 1.1.2.3.3.7.2

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

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {(x^{2} + 1)}^{\frac{1}{2} \cdot 2}}$

Step 1.1.2.3.3.7.3

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

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {(x^{2} + 1)}^{\frac{2}{2}}}$

Step 1.1.2.3.3.7.4

Cancel the common factor of $2$ .

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Step 1.1.2.3.3.7.4.1

Cancel the common factor.

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {(x^{2} + 1)}^{\frac{2}{2}}}$

Step 1.1.2.3.3.7.4.2

Rewrite the expression.

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y {(x^{2} + 1)}^{1}}$

Step 1.1.2.3.3.7.5

Simplify.

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 y (x^{2} + 1)}$

Step 1.2

Regroup factors.

$\frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 (x^{2} + 1)} \cdot \frac{1}{y}$

Step 1.3

Multiply both sides by $y$ .

$y \frac{d y}{d x} = y (\frac{7 x \sqrt{x^{2} + 1}}{8 (x^{2} + 1)} \cdot \frac{1}{y})$

Step 1.4

Simplify.

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Step 1.4.1

Combine.

$y \frac{d y}{d x} = y \frac{7 x \sqrt{x^{2} + 1} \cdot 1}{8 (x^{2} + 1) y}$

Step 1.4.2

Cancel the common factor of $y$ .

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Step 1.4.2.1

Factor $y$ out of $8 (x^{2} + 1) y$ .

$y \frac{d y}{d x} = y \frac{7 x \sqrt{x^{2} + 1} \cdot 1}{y (8 (x^{2} + 1))}$

Step 1.4.2.2

Cancel the common factor.

$y \frac{d y}{d x} = y \frac{7 x \sqrt{x^{2} + 1} \cdot 1}{y (8 (x^{2} + 1))}$

Step 1.4.2.3

Rewrite the expression.

$y \frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1} \cdot 1}{8 (x^{2} + 1)}$

Step 1.4.3

Multiply $7$ by $1$ .

$y \frac{d y}{d x} = \frac{7 x \sqrt{x^{2} + 1}}{8 (x^{2} + 1)}$

Step 1.5

Rewrite the equation.

$y d y = \frac{7 x \sqrt{x^{2} + 1}}{8 (x^{2} + 1)} d x$

Step 2

Integrate both sides.

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Step 2.1

Set up an integral on each side.

$\int y d y = \int \frac{7 x \sqrt{x^{2} + 1}}{8 (x^{2} + 1)} d x$

Step 2.2

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

$\frac{1}{2} y^{2} + C_{1} = \int \frac{7 x \sqrt{x^{2} + 1}}{8 (x^{2} + 1)} d x$

Step 2.3

Integrate the right side.

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Step 2.3.1

Since $\frac{7}{8}$ is constant with respect to $x$ , move $\frac{7}{8}$ out of the integral.

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} \int \frac{x \sqrt{x^{2} + 1}}{x^{2} + 1} d x$

Step 2.3.2

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

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Step 2.3.2.1.1

Differentiate $x^{2} + 1$ .

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

Step 2.3.2.1.2

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 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 $n = 2$ .

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

Step 2.3.2.1.4

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} \int \frac{\sqrt{u}}{u} \cdot \frac{1}{2} d u$

Step 2.3.3

Simplify.

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Step 2.3.3.1

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} \int \frac{\sqrt{u}}{u \cdot 2} d u$

Step 2.3.3.2

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} \int \frac{\sqrt{u}}{2 u} d u$

Step 2.3.4

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} (\frac{1}{2} \int \frac{\sqrt{u}}{u} d u)$

Step 2.3.5

Simplify the expression.

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Step 2.3.5.1

Simplify.

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Step 2.3.5.1.1

Multiply $\frac{1}{2}$ by $\frac{7}{8}$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{2 \cdot 8} \int \frac{\sqrt{u}}{u} d u$

Step 2.3.5.1.2

Multiply $2$ by $8$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{\sqrt{u}}{u} d u$

Step 2.3.5.2

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{u}$ as $u^{\frac{1}{2}}$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{u^{\frac{1}{2}}}{u} d u$

Step 2.3.5.3

Simplify.

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Step 2.3.5.3.1

Move $u^{\frac{1}{2}}$ to the denominator using the negative exponent rule $b^{n} = \frac{1}{b^{- n}}$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{1}{u \cdot u^{- \frac{1}{2}}} d u$

Step 2.3.5.3.2

Multiply $u$ by $u^{- \frac{1}{2}}$ by adding the exponents.

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Step 2.3.5.3.2.1

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

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Step 2.3.5.3.2.1.1

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{1}{u^{1} u^{- \frac{1}{2}}} d u$

Step 2.3.5.3.2.1.2

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{1}{u^{1 - \frac{1}{2}}} d u$

Step 2.3.5.3.2.2

Write $1$ as a fraction with a common denominator.

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{1}{u^{\frac{2}{2} - \frac{1}{2}}} d u$

Step 2.3.5.3.2.3

Combine the numerators over the common denominator.

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{1}{u^{\frac{2 - 1}{2}}} d u$

Step 2.3.5.3.2.4

Subtract $1$ from $2$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int \frac{1}{u^{\frac{1}{2}}} d u$

Step 2.3.5.4

Apply basic rules of exponents.

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Step 2.3.5.4.1

Move $u^{\frac{1}{2}}$ out of the denominator by raising it to the $- 1$ power.

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int {(u^{\frac{1}{2}})}^{- 1} d u$

Step 2.3.5.4.2

Multiply the exponents in ${(u^{\frac{1}{2}})}^{- 1}$ .

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Step 2.3.5.4.2.1

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int u^{\frac{1}{2} \cdot - 1} d u$

Step 2.3.5.4.2.2

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int u^{\frac{- 1}{2}} d u$

Step 2.3.5.4.2.3

Move the negative in front of the fraction.

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \int u^{- \frac{1}{2}} d u$

Step 2.3.6

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} (2 u^{\frac{1}{2}} + C_{2})$

Step 2.3.7

Simplify.

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Step 2.3.7.1

Rewrite $\frac{7}{16} (2 u^{\frac{1}{2}} + C_{2})$ as $\frac{7}{16} \cdot 2 u^{\frac{1}{2}} + C_{2}$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{16} \cdot 2 u^{\frac{1}{2}} + C_{2}$

Step 2.3.7.2

Simplify.

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Step 2.3.7.2.1

Combine $\frac{7}{16}$ and $2$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{7 \cdot 2}{16} u^{\frac{1}{2}} + C_{2}$

Step 2.3.7.2.2

Multiply $7$ by $2$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{14}{16} u^{\frac{1}{2}} + C_{2}$

Step 2.3.7.2.3

Cancel the common factor of $14$ and $16$ .

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Step 2.3.7.2.3.1

Factor $2$ out of $14$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{2 (7)}{16} u^{\frac{1}{2}} + C_{2}$

Step 2.3.7.2.3.2

Cancel the common factors.

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Step 2.3.7.2.3.2.1

Factor $2$ out of $16$ .

$\frac{1}{2} y^{2} + C_{1} = \frac{2 \cdot 7}{2 \cdot 8} u^{\frac{1}{2}} + C_{2}$

Step 2.3.7.2.3.2.2

Cancel the common factor.

$\frac{1}{2} y^{2} + C_{1} = \frac{2 \cdot 7}{2 \cdot 8} u^{\frac{1}{2}} + C_{2}$

Step 2.3.7.2.3.2.3

Rewrite the expression.

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} u^{\frac{1}{2}} + C_{2}$

Step 2.3.8

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

$\frac{1}{2} y^{2} + C_{1} = \frac{7}{8} {(x^{2} + 1)}^{\frac{1}{2}} + C_{2}$

Step 2.4

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

$\frac{1}{2} y^{2} = \frac{7}{8} {(x^{2} + 1)}^{\frac{1}{2}} + K$