Calculus Examples

$\frac{d y}{d x} = \frac{y}{x} + 7 x + 9$

Step 1

Rewrite the differential equation as $\frac{d y}{d x} + M (x) y = Q (x)$ .

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Step 1.1

Subtract $\frac{y}{x}$ from both sides of the equation.

$\frac{d y}{d x} - \frac{y}{x} = 7 x + 9$

Step 1.2

Factor $y$ out of $- \frac{y}{x}$ .

$\frac{d y}{d x} + y (- \frac{1}{x}) = 7 x + 9$

Step 1.3

Reorder $y$ and $- \frac{1}{x}$ .

$\frac{d y}{d x} - \frac{1}{x} y = 7 x + 9$

Step 2

The integrating factor is defined by the formula $e^{\int P (x) d x}$ , where $P (x) = - \frac{1}{x}$ .

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Step 2.1

Set up the integration.

$e^{\int - \frac{1}{x} d x}$

Step 2.2

Integrate $- \frac{1}{x}$ .

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Step 2.2.1

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

$e^{- \int \frac{1}{x} d x}$

Step 2.2.2

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

$e^{- (\ln (| x |) + C)}$

Step 2.2.3

Simplify.

$e^{- \ln (| x |) + C}$

Step 2.3

Remove the constant of integration.

$e^{- \ln (x)}$

Step 2.4

Use the logarithmic power rule.

$e^{\ln (x^{- 1})}$

Step 2.5

Exponentiation and log are inverse functions.

$x^{- 1}$

Step 2.6

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$\frac{1}{x}$

Step 3

Multiply each term by the integrating factor $\frac{1}{x}$ .

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Step 3.1

Multiply each term by $\frac{1}{x}$ .

$\frac{1}{x} \frac{d y}{d x} + \frac{1}{x} (- \frac{1}{x} y) = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2

Simplify each term.

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Step 3.2.1

Combine $\frac{1}{x}$ and $\frac{d y}{d x}$ .

$\frac{\frac{d y}{d x}}{x} + \frac{1}{x} (- \frac{1}{x} y) = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.2

Rewrite using the commutative property of multiplication.

$\frac{\frac{d y}{d x}}{x} - \frac{1}{x} (\frac{1}{x} y) = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.3

Combine $\frac{1}{x}$ and $y$ .

$\frac{\frac{d y}{d x}}{x} - \frac{1}{x} \cdot \frac{y}{x} = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.4

Multiply $- \frac{1}{x} \cdot \frac{y}{x}$ .

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Step 3.2.4.1

Multiply $\frac{y}{x}$ by $\frac{1}{x}$ .

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x \cdot x} = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.4.2

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

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{1} x} = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.4.3

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

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{1} x^{1}} = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.4.4

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

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{1 + 1}} = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.2.4.5

Add $1$ and $1$ .

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{2}} = \frac{1}{x} (7 x) + \frac{1}{x} \cdot 9$

Step 3.3

Simplify each term.

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Step 3.3.1

Rewrite using the commutative property of multiplication.

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{2}} = 7 \frac{1}{x} x + \frac{1}{x} \cdot 9$

Step 3.3.2

Combine $7$ and $\frac{1}{x}$ .

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{2}} = \frac{7}{x} x + \frac{1}{x} \cdot 9$

Step 3.3.3

Cancel the common factor of $x$ .

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Step 3.3.3.1

Cancel the common factor.

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{2}} = \frac{7}{x} x + \frac{1}{x} \cdot 9$

Step 3.3.3.2

Rewrite the expression.

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{2}} = 7 + \frac{1}{x} \cdot 9$

Step 3.3.4

Combine $\frac{1}{x}$ and $9$ .

$\frac{\frac{d y}{d x}}{x} - \frac{y}{x^{2}} = 7 + \frac{9}{x}$

Step 4

Rewrite the left side as a result of differentiating a product.

$\frac{d}{d x} [\frac{1}{x} y] = 7 + \frac{9}{x}$

Step 5

Set up an integral on each side.

$\int \frac{d}{d x} [\frac{1}{x} y] d x = \int 7 + \frac{9}{x} d x$

Step 6

Integrate the left side.

$\frac{1}{x} y = \int 7 + \frac{9}{x} d x$

Step 7

Integrate the right side.

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Step 7.1

Split the single integral into multiple integrals.

$\frac{1}{x} y = \int 7 d x + \int \frac{9}{x} d x$

Step 7.2

Apply the constant rule.

$\frac{1}{x} y = 7 x + C + \int \frac{9}{x} d x$

Step 7.3

Since $9$ is constant with respect to $x$ , move $9$ out of the integral.

$\frac{1}{x} y = 7 x + C + 9 \int \frac{1}{x} d x$

Step 7.4

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

$\frac{1}{x} y = 7 x + C + 9 (\ln (| x |) + C)$

Step 7.5

Simplify.

$\frac{1}{x} y = 7 x + 9 \ln (| x |) + C$

Step 8

Solve for $y$ .

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Step 8.1

Combine $\frac{1}{x}$ and $y$ .

$\frac{y}{x} = 7 x + 9 \ln (| x |) + C$

Step 8.2

Simplify $9 \ln (| x |)$ by moving $9$ inside the logarithm.

$\frac{y}{x} = 7 x + \ln ({| x |}^{9}) + C$

Step 8.3

Multiply both sides by $x$ .

$\frac{y}{x} x = (7 x + \ln ({| x |}^{9}) + C) x$

Step 8.4

Simplify.

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Step 8.4.1

Simplify the left side.

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Step 8.4.1.1

Cancel the common factor of $x$ .

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Step 8.4.1.1.1

Cancel the common factor.

$\frac{y}{x} x = (7 x + \ln ({| x |}^{9}) + C) x$

Step 8.4.1.1.2

Rewrite the expression.

$y = (7 x + \ln ({| x |}^{9}) + C) x$

Step 8.4.2

Simplify the right side.

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Step 8.4.2.1

Simplify $(7 x + \ln ({| x |}^{9}) + C) x$ .

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Step 8.4.2.1.1

Apply the distributive property.

$y = 7 x \cdot x + \ln ({| x |}^{9}) x + C x$

Step 8.4.2.1.2

Multiply $x$ by $x$ by adding the exponents.

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Step 8.4.2.1.2.1

Move $x$ .

$y = 7 (x \cdot x) + \ln ({| x |}^{9}) x + C x$

Step 8.4.2.1.2.2

Multiply $x$ by $x$ .

$y = 7 x^{2} + \ln ({| x |}^{9}) x + C x$

Step 8.4.2.1.3

Reorder factors in $7 x^{2} + \ln ({| x |}^{9}) x + C x$ .

$y = 7 x^{2} + x \ln ({| x |}^{9}) + C x$

Step 8.4.2.1.4

Move $x \ln ({| x |}^{9})$ .

$y = 7 x^{2} + C x + x \ln ({| x |}^{9})$