Calculus Examples

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

Step 1

To solve the differential equation, let $v = y^{1 - n}$ where $n$ is the exponent of $y^{2}$ .

$v = y^{- 1}$

Step 2

Solve the equation for $y$ .

$y = v^{- 1}$

Step 3

Take the derivative of $y$ with respect to $x$ .

$y' = v^{- 1}$

Step 4

Take the derivative of $v^{- 1}$ with respect to $x$ .

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Step 4.1

Take the derivative of $v^{- 1}$ .

$y' = \frac{d}{d x} [v^{- 1}]$

Step 4.2

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

$y' = \frac{d}{d x} [\frac{1}{v}]$

Step 4.3

Differentiate using the Quotient Rule which states that $\frac{d}{d x} [\frac{f (x)}{g (x)}]$ is $\frac{g (x) \frac{d}{d x} [f (x)] - f (x) \frac{d}{d x} [g (x)]}{{g (x)}^{2}}$ where $f (x) = 1$ and $g (x) = v$ .

$y' = \frac{v \frac{d}{d x} [1] - 1 \cdot 1 \frac{d}{d x} [v]}{v^{2}}$

Step 4.4

Differentiate using the Constant Rule.

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Step 4.4.1

Multiply $- 1$ by $1$ .

$y' = \frac{v \frac{d}{d x} [1] - \frac{d}{d x} [v]}{v^{2}}$

Step 4.4.2

Since $1$ is constant with respect to $x$ , the derivative of $1$ with respect to $x$ is $0$ .

$y' = \frac{v \cdot 0 - \frac{d}{d x} [v]}{v^{2}}$

Step 4.4.3

Simplify the expression.

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Step 4.4.3.1

Multiply $v$ by $0$ .

$y' = \frac{0 - \frac{d}{d x} [v]}{v^{2}}$

Step 4.4.3.2

Subtract $\frac{d}{d x} [v]$ from $0$ .

$y' = \frac{- \frac{d}{d x} [v]}{v^{2}}$

Step 4.4.3.3

Move the negative in front of the fraction.

$y' = - \frac{\frac{d}{d x} [v]}{v^{2}}$

Step 4.5

Rewrite $\frac{d}{d x} [v]$ as $v'$ .

$y' = - \frac{v'}{v^{2}}$

Step 5

Substitute $- \frac{v'}{v^{2}}$ for $\frac{d y}{d x}$ and $v^{- 1}$ for $y$ in the original equation $\frac{d y}{d x} - y = e^{- x} y^{2}$ .

$- \frac{v'}{v^{2}} - v^{- 1} = e^{- x} {(v^{- 1})}^{2}$

Step 6

Solve the substituted differential equation.

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Step 6.1

Multiply each term in $- \frac{\frac{d v}{d x}}{v^{2}} - v^{- 1} = e^{- x} {(v^{- 1})}^{2}$ by $- v^{2}$ to eliminate the fractions.

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Step 6.1.1

Multiply each term in $- \frac{\frac{d v}{d x}}{v^{2}} - v^{- 1} = e^{- x} {(v^{- 1})}^{2}$ by $- v^{2}$ .

$- \frac{\frac{d v}{d x}}{v^{2}} (- v^{2}) - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2

Simplify the left side.

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Step 6.1.2.1

Simplify each term.

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Step 6.1.2.1.1

Cancel the common factor of $v^{2}$ .

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Step 6.1.2.1.1.1

Move the leading negative in $- \frac{\frac{d v}{d x}}{v^{2}}$ into the numerator.

$\frac{- \frac{d v}{d x}}{v^{2}} (- v^{2}) - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.1.2

Factor $v^{2}$ out of $- v^{2}$ .

$\frac{- \frac{d v}{d x}}{v^{2}} (v^{2} \cdot - 1) - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.1.3

Cancel the common factor.

$\frac{- \frac{d v}{d x}}{v^{2}} (v^{2} \cdot - 1) - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.1.4

Rewrite the expression.

$- \frac{d v}{d x} \cdot - 1 - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.2

Multiply $- 1$ by $- 1$ .

$1 \frac{d v}{d x} - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.3

Multiply $\frac{d v}{d x}$ by $1$ .

$\frac{d v}{d x} - v^{- 1} (- v^{2}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.4

Rewrite using the commutative property of multiplication.

$\frac{d v}{d x} - 1 \cdot - 1 v^{- 1} v^{2} = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.5

Multiply $v^{- 1}$ by $v^{2}$ by adding the exponents.

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Step 6.1.2.1.5.1

Move $v^{2}$ .

$\frac{d v}{d x} - 1 \cdot - 1 (v^{2} v^{- 1}) = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.5.2

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

$\frac{d v}{d x} - 1 \cdot - 1 v^{2 - 1} = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.5.3

Subtract $1$ from $2$ .

$\frac{d v}{d x} - 1 \cdot - 1 v^{1} = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.6

Simplify $- 1 \cdot - 1 v^{1}$ .

$\frac{d v}{d x} - 1 \cdot - 1 v = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.7

Multiply $- 1$ by $- 1$ .

$\frac{d v}{d x} + 1 v = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.2.1.8

Multiply $v$ by $1$ .

$\frac{d v}{d x} + v = e^{- x} {(v^{- 1})}^{2} (- v^{2})$

Step 6.1.3

Simplify the right side.

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Step 6.1.3.1

Rewrite using the commutative property of multiplication.

$\frac{d v}{d x} + v = - e^{- x} {(v^{- 1})}^{2} v^{2}$

Step 6.1.3.2

Multiply the exponents in ${(v^{- 1})}^{2}$ .

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Step 6.1.3.2.1

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

$\frac{d v}{d x} + v = - e^{- x} v^{- 1 \cdot 2} v^{2}$

Step 6.1.3.2.2

Multiply $- 1$ by $2$ .

$\frac{d v}{d x} + v = - e^{- x} v^{- 2} v^{2}$

Step 6.1.3.3

Multiply $v^{- 2}$ by $v^{2}$ by adding the exponents.

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Step 6.1.3.3.1

Move $v^{2}$ .

$\frac{d v}{d x} + v = - e^{- x} (v^{2} v^{- 2})$

Step 6.1.3.3.2

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

$\frac{d v}{d x} + v = - e^{- x} v^{2 - 2}$

Step 6.1.3.3.3

Subtract $2$ from $2$ .

$\frac{d v}{d x} + v = - e^{- x} v^{0}$

Step 6.1.3.4

Simplify $- e^{- x} v^{0}$ .

$\frac{d v}{d x} + v = - e^{- x}$

Step 6.2

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

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Step 6.2.1

Set up the integration.

$e^{\int d x}$

Step 6.2.2

Apply the constant rule.

$e^{x + C}$

Step 6.2.3

Remove the constant of integration.

$e^{x}$

Step 6.3

Multiply each term by the integrating factor $e^{x}$ .

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Step 6.3.1

Multiply each term by $e^{x}$ .

$e^{x} \frac{d v}{d x} + e^{x} v = e^{x} (- e^{- x})$

Step 6.3.2

Rewrite using the commutative property of multiplication.

$e^{x} \frac{d v}{d x} + e^{x} v = - e^{x} e^{- x}$

Step 6.3.3

Multiply $e^{x}$ by $e^{- x}$ by adding the exponents.

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Step 6.3.3.1

Move $e^{- x}$ .

$e^{x} \frac{d v}{d x} + e^{x} v = - (e^{- x} e^{x})$

Step 6.3.3.2

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

$e^{x} \frac{d v}{d x} + e^{x} v = - e^{- x + x}$

Step 6.3.3.3

Add $- x$ and $x$ .

$e^{x} \frac{d v}{d x} + e^{x} v = - e^{0}$

Step 6.3.4

Simplify $- e^{0}$ .

$e^{x} \frac{d v}{d x} + e^{x} v = - 1$

Step 6.3.5

Reorder factors in $e^{x} \frac{d v}{d x} + e^{x} v = - 1$ .

$e^{x} \frac{d v}{d x} + v e^{x} = - 1$

Step 6.4

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

$\frac{d}{d x} [e^{x} v] = - 1$

Step 6.5

Set up an integral on each side.

$\int \frac{d}{d x} [e^{x} v] d x = \int - 1 d x$

Step 6.6

Integrate the left side.

$e^{x} v = \int - 1 d x$

Step 6.7

Apply the constant rule.

$e^{x} v = - x + C$

Step 6.8

Divide each term in $e^{x} v = - x + C$ by $e^{x}$ and simplify.

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Step 6.8.1

Divide each term in $e^{x} v = - x + C$ by $e^{x}$ .

$\frac{e^{x} v}{e^{x}} = \frac{- x}{e^{x}} + \frac{C}{e^{x}}$

Step 6.8.2

Simplify the left side.

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Step 6.8.2.1

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

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Step 6.8.2.1.1

Cancel the common factor.

$\frac{e^{x} v}{e^{x}} = \frac{- x}{e^{x}} + \frac{C}{e^{x}}$

Step 6.8.2.1.2

Divide $v$ by $1$ .

$v = \frac{- x}{e^{x}} + \frac{C}{e^{x}}$

Step 6.8.3

Simplify the right side.

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Step 6.8.3.1

Move the negative in front of the fraction.

$v = - \frac{x}{e^{x}} + \frac{C}{e^{x}}$

Step 7

Substitute $y^{- 1}$ for $v$ .

$y^{- 1} = - \frac{x}{e^{x}} + \frac{C}{e^{x}}$