Calculus Examples

$\int \frac{5 x + 2}{2 x^{2} + 7 x - 4} d x$

Step 1

Write the fraction using partial fraction decomposition.

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Step 1.1

Decompose the fraction and multiply through by the common denominator.

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Step 1.1.1

Factor by grouping.

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Step 1.1.1.1

For a polynomial of the form $a x^{2} + b x + c$ , rewrite the middle term as a sum of two terms whose product is $a \cdot c = 2 \cdot - 4 = - 8$ and whose sum is $b = 7$ .

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Step 1.1.1.1.1

Factor $7$ out of $7 x$ .

$\frac{5 x + 2}{2 x^{2} + 7 (x) - 4}$

Step 1.1.1.1.2

Rewrite $7$ as $- 1$ plus $8$

$\frac{5 x + 2}{2 x^{2} + (- 1 + 8) x - 4}$

Step 1.1.1.1.3

Apply the distributive property.

$\frac{5 x + 2}{2 x^{2} - 1 x + 8 x - 4}$

Step 1.1.1.2

Factor out the greatest common factor from each group.

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Step 1.1.1.2.1

Group the first two terms and the last two terms.

$\frac{5 x + 2}{(2 x^{2} - 1 x) + 8 x - 4}$

Step 1.1.1.2.2

Factor out the greatest common factor (GCF) from each group.

$\frac{5 x + 2}{x (2 x - 1) + 4 (2 x - 1)}$

Step 1.1.1.3

Factor the polynomial by factoring out the greatest common factor, $2 x - 1$ .

$\frac{5 x + 2}{(2 x - 1) (x + 4)}$

Step 1.1.2

For each factor in the denominator, create a new fraction using the factor as the denominator, and an unknown value as the numerator. Since the factor in the denominator is linear, put a single variable in its place $A$ .

$\frac{A}{2 x - 1}$

Step 1.1.3

$\frac{A}{2 x - 1} + \frac{B}{x + 4}$

Step 1.1.4

Multiply each fraction in the equation by the denominator of the original expression. In this case, the denominator is $(2 x - 1) (x + 4)$ .

$\frac{(5 x + 2) (2 x - 1) (x + 4)}{(2 x - 1) (x + 4)} = \frac{(A) (2 x - 1) (x + 4)}{2 x - 1} + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.5

Cancel the common factor of $2 x - 1$ .

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Step 1.1.5.1

Cancel the common factor.

$\frac{(5 x + 2) (2 x - 1) (x + 4)}{(2 x - 1) (x + 4)} = \frac{(A) (2 x - 1) (x + 4)}{2 x - 1} + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.5.2

Rewrite the expression.

$\frac{(5 x + 2) (x + 4)}{x + 4} = \frac{(A) (2 x - 1) (x + 4)}{2 x - 1} + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.6

Cancel the common factor of $x + 4$ .

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Step 1.1.6.1

Cancel the common factor.

$\frac{(5 x + 2) (x + 4)}{x + 4} = \frac{(A) (2 x - 1) (x + 4)}{2 x - 1} + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.6.2

Divide $5 x + 2$ by $1$ .

$5 x + 2 = \frac{(A) (2 x - 1) (x + 4)}{2 x - 1} + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.7

Simplify each term.

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Step 1.1.7.1

Cancel the common factor of $2 x - 1$ .

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Step 1.1.7.1.1

Cancel the common factor.

$5 x + 2 = \frac{A (2 x - 1) (x + 4)}{2 x - 1} + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.7.1.2

Divide $(A) (x + 4)$ by $1$ .

$5 x + 2 = (A) (x + 4) + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.7.2

Apply the distributive property.

$5 x + 2 = A x + A \cdot 4 + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.7.3

Move $4$ to the left of $A$ .

$5 x + 2 = A x + 4 \cdot A + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.7.4

Cancel the common factor of $x + 4$ .

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Step 1.1.7.4.1

Cancel the common factor.

$5 x + 2 = A x + 4 A + \frac{(B) (2 x - 1) (x + 4)}{x + 4}$

Step 1.1.7.4.2

Divide $(B) (2 x - 1)$ by $1$ .

$5 x + 2 = A x + 4 A + (B) (2 x - 1)$

Step 1.1.7.5

Apply the distributive property.

$5 x + 2 = A x + 4 A + B (2 x) + B \cdot - 1$

Step 1.1.7.6

Rewrite using the commutative property of multiplication.

$5 x + 2 = A x + 4 A + 2 B x + B \cdot - 1$

Step 1.1.7.7

Move $- 1$ to the left of $B$ .

$5 x + 2 = A x + 4 A + 2 B x - 1 \cdot B$

Step 1.1.7.8

Rewrite $- 1 B$ as $- B$ .

$5 x + 2 = A x + 4 A + 2 B x - B$

Step 1.1.8

Simplify the expression.

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Step 1.1.8.1

Move $B$ .

$5 x + 2 = A x + 4 A + 2 x B - B$

Step 1.1.8.2

Move $4 A$ .

$5 x + 2 = A x + 2 x B + 4 A - B$

Step 1.2

Create equations for the partial fraction variables and use them to set up a system of equations.

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Step 1.2.1

Create an equation for the partial fraction variables by equating the coefficients of $x$ from each side of the equation. For the equation to be equal, the equivalent coefficients on each side of the equation must be equal.

$5 = A + 2 B$

Step 1.2.2

Create an equation for the partial fraction variables by equating the coefficients of the terms not containing $x$ . For the equation to be equal, the equivalent coefficients on each side of the equation must be equal.

$2 = 4 A - 1 B$

Step 1.2.3

Set up the system of equations to find the coefficients of the partial fractions.

$5 = A + 2 B$

$2 = 4 A - 1 B$

$5 = A + 2 B$

$2 = 4 A - 1 B$

Step 1.3

Solve the system of equations.

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Step 1.3.1

Solve for $A$ in $5 = A + 2 B$ .

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Step 1.3.1.1

Rewrite the equation as $A + 2 B = 5$ .

$A + 2 B = 5$

$2 = 4 A - 1 B$

Step 1.3.1.2

Subtract $2 B$ from both sides of the equation.

$A = 5 - 2 B$

$2 = 4 A - 1 B$

$A = 5 - 2 B$

$2 = 4 A - 1 B$

Step 1.3.2

Replace all occurrences of $A$ with $5 - 2 B$ in each equation.

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Step 1.3.2.1

Replace all occurrences of $A$ in $2 = 4 A - 1 B$ with $5 - 2 B$ .

$2 = 4 (5 - 2 B) - 1 B$

$A = 5 - 2 B$

Step 1.3.2.2

Simplify the right side.

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Step 1.3.2.2.1

Simplify $4 (5 - 2 B) - 1 B$ .

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Step 1.3.2.2.1.1

Simplify each term.

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Step 1.3.2.2.1.1.1

Apply the distributive property.

$2 = 4 \cdot 5 + 4 (- 2 B) - 1 B$

$A = 5 - 2 B$

Step 1.3.2.2.1.1.2

Multiply $4$ by $5$ .

$2 = 20 + 4 (- 2 B) - 1 B$

$A = 5 - 2 B$

Step 1.3.2.2.1.1.3

Multiply $- 2$ by $4$ .

$2 = 20 - 8 B - 1 B$

$A = 5 - 2 B$

Step 1.3.2.2.1.1.4

Rewrite $- 1 B$ as $- B$ .

$2 = 20 - 8 B - B$

$A = 5 - 2 B$

$2 = 20 - 8 B - B$

$A = 5 - 2 B$

Step 1.3.2.2.1.2

Subtract $B$ from $- 8 B$ .

$2 = 20 - 9 B$

$A = 5 - 2 B$

$2 = 20 - 9 B$

$A = 5 - 2 B$

$2 = 20 - 9 B$

$A = 5 - 2 B$

$2 = 20 - 9 B$

$A = 5 - 2 B$

Step 1.3.3

Solve for $B$ in $2 = 20 - 9 B$ .

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Step 1.3.3.1

Rewrite the equation as $20 - 9 B = 2$ .

$20 - 9 B = 2$

$A = 5 - 2 B$

Step 1.3.3.2

Move all terms not containing $B$ to the right side of the equation.

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Step 1.3.3.2.1

Subtract $20$ from both sides of the equation.

$- 9 B = 2 - 20$

$A = 5 - 2 B$

Step 1.3.3.2.2

Subtract $20$ from $2$ .

$- 9 B = - 18$

$A = 5 - 2 B$

$- 9 B = - 18$

$A = 5 - 2 B$

Step 1.3.3.3

Divide each term in $- 9 B = - 18$ by $- 9$ and simplify.

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Step 1.3.3.3.1

Divide each term in $- 9 B = - 18$ by $- 9$ .

$\frac{- 9 B}{- 9} = \frac{- 18}{- 9}$

$A = 5 - 2 B$

Step 1.3.3.3.2

Simplify the left side.

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Step 1.3.3.3.2.1

Cancel the common factor of $- 9$ .

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Step 1.3.3.3.2.1.1

Cancel the common factor.

$\frac{- 9 B}{- 9} = \frac{- 18}{- 9}$

$A = 5 - 2 B$

Step 1.3.3.3.2.1.2

Divide $B$ by $1$ .

$B = \frac{- 18}{- 9}$

$A = 5 - 2 B$

$B = \frac{- 18}{- 9}$

$A = 5 - 2 B$

$B = \frac{- 18}{- 9}$

$A = 5 - 2 B$

Step 1.3.3.3.3

Simplify the right side.

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Step 1.3.3.3.3.1

Divide $- 18$ by $- 9$ .

$B = 2$

$A = 5 - 2 B$

$B = 2$

$A = 5 - 2 B$

$B = 2$

$A = 5 - 2 B$

$B = 2$

$A = 5 - 2 B$

Step 1.3.4

Replace all occurrences of $B$ with $2$ in each equation.

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Step 1.3.4.1

Replace all occurrences of $B$ in $A = 5 - 2 B$ with $2$ .

$A = 5 - 2 \cdot 2$

$B = 2$

Step 1.3.4.2

Simplify the right side.

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Step 1.3.4.2.1

Simplify $5 - 2 \cdot 2$ .

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Step 1.3.4.2.1.1

Multiply $- 2$ by $2$ .

$A = 5 - 4$

$B = 2$

Step 1.3.4.2.1.2

Subtract $4$ from $5$ .

$A = 1$

$B = 2$

$A = 1$

$B = 2$

$A = 1$

$B = 2$

$A = 1$

$B = 2$

Step 1.3.5

List all of the solutions.

$A = 1, B = 2$

Step 1.4

Replace each of the partial fraction coefficients in $\frac{A}{2 x - 1} + \frac{B}{x + 4}$ with the values found for $A$ and $B$ .

$\frac{1}{2 x - 1} + \frac{2}{x + 4}$

Step 1.5

Remove the zero from the expression.

$\int \frac{1}{2 x - 1} + \frac{2}{x + 4} d x$

Step 2

Split the single integral into multiple integrals.

$\int \frac{1}{2 x - 1} d x + \int \frac{2}{x + 4} d x$

Step 3

Let $u_{1} = 2 x - 1$ . Then $d u_{1} = 2 d x$ , so $\frac{1}{2} d u_{1} = d x$ . Rewrite using $u_{1}$ and $d$ $u_{1}$ .

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Step 3.1

Let $u_{1} = 2 x - 1$ . Find $\frac{d u_{1}}{d x}$ .

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Step 3.1.1

Differentiate $2 x - 1$ .

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

Step 3.1.2

By the Sum Rule, the derivative of $2 x - 1$ with respect to $x$ is $\frac{d}{d x} [2 x] + \frac{d}{d x} [- 1]$ .

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

Step 3.1.3

Evaluate $\frac{d}{d x} [2 x]$ .

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Step 3.1.3.1

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

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

Step 3.1.3.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

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

Step 3.1.3.3

Multiply $2$ by $1$ .

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

Step 3.1.4

Differentiate using the Constant Rule.

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Step 3.1.4.1

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

$2 + 0$

Step 3.1.4.2

Add $2$ and $0$ .

$2$

Step 3.2

Rewrite the problem using $u_{1}$ and $d u_{1}$ .

$\int \frac{1}{u_{1}} \cdot \frac{1}{2} d u_{1} + \int \frac{2}{x + 4} d x$

Step 4

Simplify.

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Step 4.1

Multiply $\frac{1}{u_{1}}$ by $\frac{1}{2}$ .

$\int \frac{1}{u_{1} \cdot 2} d u_{1} + \int \frac{2}{x + 4} d x$

Step 4.2

Move $2$ to the left of $u_{1}$ .

$\int \frac{1}{2 u_{1}} d u_{1} + \int \frac{2}{x + 4} d x$

Step 5

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

$\frac{1}{2} \int \frac{1}{u_{1}} d u_{1} + \int \frac{2}{x + 4} d x$

Step 6

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

$\frac{1}{2} (\ln (| u_{1} |) + C) + \int \frac{2}{x + 4} d x$

Step 7

Since $2$ is constant with respect to $x$ , move $2$ out of the integral.

$\frac{1}{2} (\ln (| u_{1} |) + C) + 2 \int \frac{1}{x + 4} d x$

Step 8

Let $u_{2} = x + 4$ . Then $d u_{2} = d x$ . Rewrite using $u_{2}$ and $d$ $u_{2}$ .

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Step 8.1

Let $u_{2} = x + 4$ . Find $\frac{d u_{2}}{d x}$ .

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Step 8.1.1

Differentiate $x + 4$ .

$\frac{d}{d x} [x + 4]$

Step 8.1.2

By the Sum Rule, the derivative of $x + 4$ with respect to $x$ is $\frac{d}{d x} [x] + \frac{d}{d x} [4]$ .

$\frac{d}{d x} [x] + \frac{d}{d x} [4]$

Step 8.1.3

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$1 + \frac{d}{d x} [4]$

Step 8.1.4

Since $4$ is constant with respect to $x$ , the derivative of $4$ with respect to $x$ is $0$ .

$1 + 0$

Step 8.1.5

Add $1$ and $0$ .

$1$

Step 8.2

Rewrite the problem using $u_{2}$ and $d u_{2}$ .

$\frac{1}{2} (\ln (| u_{1} |) + C) + 2 \int \frac{1}{u_{2}} d u_{2}$

Step 9

The integral of $\frac{1}{u_{2}}$ with respect to $u_{2}$ is $\ln (| u_{2} |)$ .

$\frac{1}{2} (\ln (| u_{1} |) + C) + 2 (\ln (| u_{2} |) + C)$

Step 10

Simplify.

$\frac{1}{2} \ln (| u_{1} |) + 2 \ln (| u_{2} |) + C$

Step 11

Substitute back in for each integration substitution variable.

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Step 11.1

Replace all occurrences of $u_{1}$ with $2 x - 1$ .

$\frac{1}{2} \ln (| 2 x - 1 |) + 2 \ln (| u_{2} |) + C$

Step 11.2

Replace all occurrences of $u_{2}$ with $x + 4$ .

$\frac{1}{2} \ln (| 2 x - 1 |) + 2 \ln (| x + 4 |) + C$