Calculus Examples

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

Step 1

Add $y$ to both sides of the equation.

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

Step 2

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

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Step 2.1

Set up the integration.

$e^{\int d x}$

Step 2.2

Apply the constant rule.

$e^{x + C}$

Step 2.3

Remove the constant of integration.

$e^{x}$

Step 3

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

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Step 3.1

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

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

Step 3.2

Rewrite using the commutative property of multiplication.

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

Step 3.3

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

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

Step 4

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

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

Step 5

Set up an integral on each side.

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

Step 6

Integrate the left side.

$e^{x} y = \int - x e^{x} d x$

Step 7

Integrate the right side.

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Step 7.1

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

$e^{x} y = - \int x e^{x} d x$

Step 7.2

Integrate by parts using the formula $\int u d v = u v - \int v d u$ , where $u = x$ and $d v = e^{x}$ .

$e^{x} y = - (x e^{x} - \int e^{x} d x)$

Step 7.3

The integral of $e^{x}$ with respect to $x$ is $e^{x}$ .

$e^{x} y = - (x e^{x} - (e^{x} + C))$

Step 7.4

Simplify.

$e^{x} y = - (x e^{x} - e^{x}) + C$

Step 8

Solve for $y$ .

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Step 8.1

Simplify.

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Step 8.1.1

Apply the distributive property.

$e^{x} y = - (x e^{x}) - - e^{x} + C$

Step 8.1.2

Multiply $- - e^{x}$ .

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Step 8.1.2.1

Multiply $- 1$ by $- 1$ .

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

Step 8.1.2.2

Multiply $e^{x}$ by $1$ .

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

Step 8.2

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

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Step 8.2.1

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

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

Step 8.2.2

Simplify the left side.

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Step 8.2.2.1

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

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Step 8.2.2.1.1

Cancel the common factor.

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

Step 8.2.2.1.2

Divide $y$ by $1$ .

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

Step 8.2.3

Simplify the right side.

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Step 8.2.3.1

Simplify each term.

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Step 8.2.3.1.1

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

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Step 8.2.3.1.1.1

Cancel the common factor.

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

Step 8.2.3.1.1.2

Divide $- x$ by $1$ .

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

Step 8.2.3.1.2

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

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Step 8.2.3.1.2.1

Cancel the common factor.

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

Step 8.2.3.1.2.2

Rewrite the expression.

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