Calculus Examples

$\frac{x d y}{d x} = 4 y$

Step 1

Separate the variables.

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Step 1.1

Factor $\frac{d y}{d x}$ out.

$x \frac{d y}{d x} = 4 y$

Step 1.2

Divide each term in $x \frac{d y}{d x} = 4 y$ by $x$ and simplify.

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Step 1.2.1

Divide each term in $x \frac{d y}{d x} = 4 y$ by $x$ .

$\frac{x \frac{d y}{d x}}{x} = \frac{4 y}{x}$

Step 1.2.2

Simplify the left side.

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Step 1.2.2.1

Cancel the common factor of $x$ .

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Step 1.2.2.1.1

Cancel the common factor.

$\frac{x \frac{d y}{d x}}{x} = \frac{4 y}{x}$

Step 1.2.2.1.2

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

$\frac{d y}{d x} = \frac{4 y}{x}$

Step 1.3

Multiply both sides by $\frac{1}{y}$ .

$\frac{1}{y} \frac{d y}{d x} = \frac{1}{y} \cdot \frac{4 y}{x}$

Step 1.4

Cancel the common factor of $y$ .

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Step 1.4.1

Factor $y$ out of $4 y$ .

$\frac{1}{y} \frac{d y}{d x} = \frac{1}{y} \cdot \frac{y \cdot 4}{x}$

Step 1.4.2

Cancel the common factor.

$\frac{1}{y} \frac{d y}{d x} = \frac{1}{y} \cdot \frac{y \cdot 4}{x}$

Step 1.4.3

Rewrite the expression.

$\frac{1}{y} \frac{d y}{d x} = \frac{4}{x}$

Step 1.5

Rewrite the equation.

$\frac{1}{y} d y = \frac{4}{x} d x$

Step 2

Integrate both sides.

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Step 2.1

Set up an integral on each side.

$\int \frac{1}{y} d y = \int \frac{4}{x} d x$

Step 2.2

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

$\ln (| y |) + C_{1} = \int \frac{4}{x} d x$

Step 2.3

Integrate the right side.

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Step 2.3.1

Since $4$ is constant with respect to $x$ , move $4$ out of the integral.

$\ln (| y |) + C_{1} = 4 \int \frac{1}{x} d x$

Step 2.3.2

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

$\ln (| y |) + C_{1} = 4 (\ln (| x |) + C_{2})$

Step 2.3.3

Simplify.

$\ln (| y |) + C_{1} = 4 \ln (| x |) + C_{2}$

Step 2.4

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

$\ln (| y |) = 4 \ln (| x |) + C$

Step 3

Solve for $y$ .

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Step 3.1

Move all the terms containing a logarithm to the left side of the equation.

$\ln (| y |) - 4 \ln (| x |) = C$

Step 3.2

Simplify the left side.

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Step 3.2.1

Simplify $\ln (| y |) - 4 \ln (| x |)$ .

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Step 3.2.1.1

Simplify each term.

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Step 3.2.1.1.1

Simplify $- 4 \ln (| x |)$ by moving $4$ inside the logarithm.

$\ln (| y |) - \ln ({| x |}^{4}) = C$

Step 3.2.1.1.2

Remove the absolute value in ${| x |}^{4}$ because exponentiations with even powers are always positive.

$\ln (| y |) - \ln (x^{4}) = C$

Step 3.2.1.2

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

$\ln (\frac{| y |}{x^{4}}) = C$

Step 3.3

To solve for $y$ , rewrite the equation using properties of logarithms.

$e^{\ln (\frac{| y |}{x^{4}})} = e^{C}$

Step 3.4

Rewrite $\ln (\frac{| y |}{x^{4}}) = C$ in exponential form using the definition of a logarithm. If $x$ and $b$ are positive real numbers and $b \neq 1$ , then $\log_{b} (x) = y$ is equivalent to $b^{y} = x$ .

$e^{C} = \frac{| y |}{x^{4}}$

Step 3.5

Solve for $y$ .

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Step 3.5.1

Rewrite the equation as $\frac{| y |}{x^{4}} = e^{C}$ .

$\frac{| y |}{x^{4}} = e^{C}$

Step 3.5.2

Multiply both sides by $x^{4}$ .

$\frac{| y |}{x^{4}} x^{4} = e^{C} x^{4}$

Step 3.5.3

Simplify.

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Step 3.5.3.1

Simplify the left side.

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Step 3.5.3.1.1

Cancel the common factor of $x^{4}$ .

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Step 3.5.3.1.1.1

Cancel the common factor.

$\frac{| y |}{x^{4}} x^{4} = e^{C} x^{4}$

Step 3.5.3.1.1.2

Rewrite the expression.

$| y | = e^{C} x^{4}$

Step 3.5.3.2

Simplify the right side.

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Step 3.5.3.2.1

Reorder factors in $e^{C} x^{4}$ .

$| y | = x^{4} e^{C}$

Step 3.5.4

Remove the absolute value term. This creates a $\pm$ on the right side of the equation because $| x | = \pm x$ .

$y = \pm x^{4} e^{C}$

Step 4

Group the constant terms together.

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Step 4.1

Simplify the constant of integration.

$y = \pm x^{4} C$

Step 4.2

Combine constants with the plus or minus.

$y = C x^{4}$