Pre-Algebra Examples

$\frac{x^{2} - 49}{x^{2} - 12 x + 36} \div \frac{4 x - 28}{x^{2} - 5 x - 6}$

Step 1

To divide by a fraction, multiply by its reciprocal.

$\frac{x^{2} - 49}{x^{2} - 12 x + 36} \cdot \frac{x^{2} - 5 x - 6}{4 x - 28}$

Step 2

Simplify the numerator.

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Step 2.1

Rewrite $49$ as $7^{2}$ .

$\frac{x^{2} - 7^{2}}{x^{2} - 12 x + 36} \cdot \frac{x^{2} - 5 x - 6}{4 x - 28}$

Step 2.2

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 $b = 7$ .

$\frac{(x + 7) (x - 7)}{x^{2} - 12 x + 36} \cdot \frac{x^{2} - 5 x - 6}{4 x - 28}$

Step 3

Factor using the perfect square rule.

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Step 3.1

Rewrite $36$ as $6^{2}$ .

$\frac{(x + 7) (x - 7)}{x^{2} - 12 x + 6^{2}} \cdot \frac{x^{2} - 5 x - 6}{4 x - 28}$

Step 3.2

Check that the middle term is two times the product of the numbers being squared in the first term and third term.

$12 x = 2 \cdot x \cdot 6$

Step 3.3

Rewrite the polynomial.

$\frac{(x + 7) (x - 7)}{x^{2} - 2 \cdot x \cdot 6 + 6^{2}} \cdot \frac{x^{2} - 5 x - 6}{4 x - 28}$

Step 3.4

Factor using the perfect square trinomial rule $a^{2} - 2 a b + b^{2} = {(a - b)}^{2}$ , where $a = x$ and $b = 6$ .

$\frac{(x + 7) (x - 7)}{{(x - 6)}^{2}} \cdot \frac{x^{2} - 5 x - 6}{4 x - 28}$

Step 4

Factor $x^{2} - 5 x - 6$ 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 $- 6$ and whose sum is $- 5$ .

$- 6, 1$

Step 4.2

Write the factored form using these integers.

$\frac{(x + 7) (x - 7)}{{(x - 6)}^{2}} \cdot \frac{(x - 6) (x + 1)}{4 x - 28}$

Step 5

Factor $4$ out of $4 x - 28$ .

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Step 5.1

Factor $4$ out of $4 x$ .

$\frac{(x + 7) (x - 7)}{{(x - 6)}^{2}} \cdot \frac{(x - 6) (x + 1)}{4 (x) - 28}$

Step 5.2

Factor $4$ out of $- 28$ .

$\frac{(x + 7) (x - 7)}{{(x - 6)}^{2}} \cdot \frac{(x - 6) (x + 1)}{4 x + 4 \cdot - 7}$

Step 5.3

Factor $4$ out of $4 x + 4 \cdot - 7$ .

$\frac{(x + 7) (x - 7)}{{(x - 6)}^{2}} \cdot \frac{(x - 6) (x + 1)}{4 (x - 7)}$

Step 6

Combine.

$\frac{(x + 7) (x - 7) ((x - 6) (x + 1))}{{(x - 6)}^{2} (4 (x - 7))}$

Step 7

Cancel the common factor of $x - 7$ .

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Step 7.1

Cancel the common factor.

$\frac{(x + 7) (x - 7) ((x - 6) (x + 1))}{{(x - 6)}^{2} (4 (x - 7))}$

Step 7.2

Rewrite the expression.

$\frac{(x + 7) ((x - 6) (x + 1))}{{(x - 6)}^{2} \cdot (4)}$

Step 8

Cancel the common factor of $x - 6$ and ${(x - 6)}^{2}$ .

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Step 8.1

Factor $x - 6$ out of $(x + 7) ((x - 6) (x + 1))$ .

$\frac{(x - 6) ((x + 7) (x + 1))}{{(x - 6)}^{2} \cdot (4)}$

Step 8.2

Cancel the common factors.

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Step 8.2.1

Factor $x - 6$ out of ${(x - 6)}^{2} \cdot (4)$ .

$\frac{(x - 6) ((x + 7) (x + 1))}{(x - 6) ((x - 6) \cdot 4)}$

Step 8.2.2

Cancel the common factor.

$\frac{(x - 6) ((x + 7) (x + 1))}{(x - 6) ((x - 6) \cdot 4)}$

Step 8.2.3

Rewrite the expression.

$\frac{(x + 7) (x + 1)}{(x - 6) \cdot 4}$

Step 9

Move $4$ to the left of $x - 6$ .

$\frac{(x + 7) (x + 1)}{4 (x - 6)}$