How to add rational expressions with different denominators

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SAT Math › How to add rational expressions with different denominators

Questions 1 - 2

Simplify the expression.

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

$\frac{2x}{3x+6}$

$\frac{3x}{2x+4}$

$\frac{x}{x+2}$

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

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

Explanation

To add rational expressions, first find the least common denominator. Because the denominator of the first fraction factors to 2(x+2), it is clear that this is the common denominator. Therefore, multiply the numerator and denominator of the second fraction by 2.

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

$\frac{x}{2x+4}+\frac{(2)x}{(2)(x+2)}$

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

$\frac{3x}{2x+4}$

This is the most simplified version of the rational expression.

Simplify the following:

$\frac{x+3}{x-2}+\frac{x-2}{x+3}$

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

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

Explanation

To simplify the following, a common denominator must be achieved. In this case, the first term must be multiplied by (x+2) in both the numerator and denominator and likewise with the second term with (x-3).

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

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

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