Pre-Algebra Examples

$\frac{7 x}{3 x^{2} - 2 x - 16} - \frac{2 x}{x^{2} + x - 2}$

Step 1

Simplify each term.

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Step 1.1

Factor by grouping.

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Step 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 $a \cdot c = 3 \cdot - 16 = - 48$ and whose sum is $b = - 2$ .

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Step 1.1.1.1

Factor $- 2$ out of $- 2 x$ .

$\frac{7 x}{3 x^{2} - 2 (x) - 16} - \frac{2 x}{x^{2} + x - 2}$

Step 1.1.1.2

Rewrite $- 2$ as $6$ plus $- 8$

$\frac{7 x}{3 x^{2} + (6 - 8) x - 16} - \frac{2 x}{x^{2} + x - 2}$

Step 1.1.1.3

Apply the distributive property.

$\frac{7 x}{3 x^{2} + 6 x - 8 x - 16} - \frac{2 x}{x^{2} + x - 2}$

Step 1.1.2

Factor out the greatest common factor from each group.

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Step 1.1.2.1

Group the first two terms and the last two terms.

$\frac{7 x}{(3 x^{2} + 6 x) - 8 x - 16} - \frac{2 x}{x^{2} + x - 2}$

Step 1.1.2.2

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

$\frac{7 x}{3 x (x + 2) - 8 (x + 2)} - \frac{2 x}{x^{2} + x - 2}$

Step 1.1.3

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

$\frac{7 x}{(x + 2) (3 x - 8)} - \frac{2 x}{x^{2} + x - 2}$

Step 1.2

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

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Step 1.2.1

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 $- 2$ and whose sum is $1$ .

$- 1, 2$

Step 1.2.2

Write the factored form using these integers.

$\frac{7 x}{(x + 2) (3 x - 8)} - \frac{2 x}{(x - 1) (x + 2)}$

Step 2

To write $\frac{7 x}{(x + 2) (3 x - 8)}$ as a fraction with a common denominator, multiply by $\frac{x - 1}{x - 1}$ .

$\frac{7 x}{(x + 2) (3 x - 8)} \cdot \frac{x - 1}{x - 1} - \frac{2 x}{(x - 1) (x + 2)}$

Step 3

To write $- \frac{2 x}{(x - 1) (x + 2)}$ as a fraction with a common denominator, multiply by $\frac{3 x - 8}{3 x - 8}$ .

$\frac{7 x}{(x + 2) (3 x - 8)} \cdot \frac{x - 1}{x - 1} - \frac{2 x}{(x - 1) (x + 2)} \cdot \frac{3 x - 8}{3 x - 8}$

Step 4

Write each expression with a common denominator of $(x + 2) (3 x - 8) (x - 1)$ , by multiplying each by an appropriate factor of $1$ .

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Step 4.1

Multiply $\frac{7 x}{(x + 2) (3 x - 8)}$ by $\frac{x - 1}{x - 1}$ .

$\frac{7 x (x - 1)}{(x + 2) (3 x - 8) (x - 1)} - \frac{2 x}{(x - 1) (x + 2)} \cdot \frac{3 x - 8}{3 x - 8}$

Step 4.2

Multiply $\frac{2 x}{(x - 1) (x + 2)}$ by $\frac{3 x - 8}{3 x - 8}$ .

$\frac{7 x (x - 1)}{(x + 2) (3 x - 8) (x - 1)} - \frac{2 x (3 x - 8)}{(x - 1) (x + 2) (3 x - 8)}$

Step 4.3

Reorder the factors of $(x + 2) (3 x - 8) (x - 1)$ .

$\frac{7 x (x - 1)}{(3 x - 8) (x + 2) (x - 1)} - \frac{2 x (3 x - 8)}{(x - 1) (x + 2) (3 x - 8)}$

Step 4.4

Reorder the factors of $(x - 1) (x + 2) (3 x - 8)$ .

$\frac{7 x (x - 1)}{(3 x - 8) (x + 2) (x - 1)} - \frac{2 x (3 x - 8)}{(3 x - 8) (x + 2) (x - 1)}$

Step 5

Combine the numerators over the common denominator.

$\frac{7 x (x - 1) - 2 x (3 x - 8)}{(3 x - 8) (x + 2) (x - 1)}$

Step 6

Simplify the numerator.

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Step 6.1

Factor $x$ out of $7 x (x - 1) - 2 x (3 x - 8)$ .

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Step 6.1.1

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

$\frac{x (7 (x - 1)) - 2 x (3 x - 8)}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.1.2

Factor $x$ out of $- 2 x (3 x - 8)$ .

$\frac{x (7 (x - 1)) + x (- 2 (3 x - 8))}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.1.3

Factor $x$ out of $x (7 (x - 1)) + x (- 2 (3 x - 8))$ .

$\frac{x (7 (x - 1) - 2 (3 x - 8))}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.2

Apply the distributive property.

$\frac{x (7 x + 7 \cdot - 1 - 2 (3 x - 8))}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.3

Multiply $7$ by $- 1$ .

$\frac{x (7 x - 7 - 2 (3 x - 8))}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.4

Apply the distributive property.

$\frac{x (7 x - 7 - 2 (3 x) - 2 \cdot - 8)}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.5

Multiply $3$ by $- 2$ .

$\frac{x (7 x - 7 - 6 x - 2 \cdot - 8)}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.6

Multiply $- 2$ by $- 8$ .

$\frac{x (7 x - 7 - 6 x + 16)}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.7

Subtract $6 x$ from $7 x$ .

$\frac{x (x - 7 + 16)}{(3 x - 8) (x + 2) (x - 1)}$

Step 6.8

Add $- 7$ and $16$ .

$\frac{x (x + 9)}{(3 x - 8) (x + 2) (x - 1)}$