Precalculus Examples

$\frac{\frac{2 x^{2} - 7 x - 4}{x^{2} - 9}}{\frac{2 x^{2} + 9 x + 4}{x^{2} + x - 12}}$

Step 1

Multiply the numerator by the reciprocal of the denominator.

$\frac{2 x^{2} - 7 x - 4}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2

Factor by grouping.

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Step 2.1

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 2.1.1

Factor $- 7$ out of $- 7 x$ .

$\frac{2 x^{2} - 7 (x) - 4}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2.1.2

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

$\frac{2 x^{2} + (1 - 8) x - 4}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2.1.3

Apply the distributive property.

$\frac{2 x^{2} + 1 x - 8 x - 4}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2.1.4

Multiply $x$ by $1$ .

$\frac{2 x^{2} + x - 8 x - 4}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2.2

Factor out the greatest common factor from each group.

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Step 2.2.1

Group the first two terms and the last two terms.

$\frac{(2 x^{2} + x) - 8 x - 4}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2.2.2

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

$\frac{x (2 x + 1) - 4 (2 x + 1)}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 2.3

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

$\frac{(2 x + 1) (x - 4)}{x^{2} - 9} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 3

Simplify the denominator.

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Step 3.1

Rewrite $9$ as $3^{2}$ .

$\frac{(2 x + 1) (x - 4)}{x^{2} - 3^{2}} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 3.2

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = x$ and $b = 3$ .

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{x^{2} + x - 12}{2 x^{2} + 9 x + 4}$

Step 4

Factor $x^{2} + x - 12$ using the AC method.

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Step 4.1

Consider the form $x^{2} + b x + c$ . Find a pair of integers whose product is $c$ and whose sum is $b$ . In this case, whose product is $- 12$ and whose sum is $1$ .

$- 3, 4$

Step 4.2

Write the factored form using these integers.

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{2 x^{2} + 9 x + 4}$

Step 5

Factor by grouping.

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Step 5.1

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 $b = 9$ .

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Step 5.1.1

Factor $9$ out of $9 x$ .

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{2 x^{2} + 9 (x) + 4}$

Step 5.1.2

Rewrite $9$ as $1$ plus $8$

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{2 x^{2} + (1 + 8) x + 4}$

Step 5.1.3

Apply the distributive property.

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{2 x^{2} + 1 x + 8 x + 4}$

Step 5.1.4

Multiply $x$ by $1$ .

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{2 x^{2} + x + 8 x + 4}$

Step 5.2

Factor out the greatest common factor from each group.

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Step 5.2.1

Group the first two terms and the last two terms.

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{(2 x^{2} + x) + 8 x + 4}$

Step 5.2.2

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

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{x (2 x + 1) + 4 (2 x + 1)}$

Step 5.3

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

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{(2 x + 1) (x + 4)}$

Step 6

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

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Step 6.1

Cancel the common factor.

$\frac{(2 x + 1) (x - 4)}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{(2 x + 1) (x + 4)}$

Step 6.2

Rewrite the expression.

$\frac{x - 4}{(x + 3) (x - 3)} \cdot \frac{(x - 3) (x + 4)}{x + 4}$

Step 7

Cancel the common factor of $x - 3$ .

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Step 7.1

Factor $x - 3$ out of $(x + 3) (x - 3)$ .

$\frac{x - 4}{(x - 3) (x + 3)} \cdot \frac{(x - 3) (x + 4)}{x + 4}$

Step 7.2

Cancel the common factor.

$\frac{x - 4}{(x - 3) (x + 3)} \cdot \frac{(x - 3) (x + 4)}{x + 4}$

Step 7.3

Rewrite the expression.

$\frac{x - 4}{x + 3} \cdot \frac{x + 4}{x + 4}$

Step 8

Multiply $\frac{x - 4}{x + 3}$ by $\frac{x + 4}{x + 4}$ .

$\frac{(x - 4) (x + 4)}{(x + 3) (x + 4)}$

Step 9

Cancel the common factor of $x + 4$ .

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Step 9.1

Cancel the common factor.

$\frac{(x - 4) (x + 4)}{(x + 3) (x + 4)}$

Step 9.2

Rewrite the expression.

$\frac{x - 4}{x + 3}$