Example

Try It 7.60: Simplifying 2x71x+76x+71x249\frac{\frac{2}{x-7}-\frac{1}{x+7}}{\frac{6}{x+7}-\frac{1}{x^2-49}} Using the LCD

To simplify the complex rational expression 2x71x+76x+71x249\frac{\frac{2}{x-7}-\frac{1}{x+7}}{\frac{6}{x+7}-\frac{1}{x^2-49}} using the least common denominator (LCD) method:

Step 1. Find the LCD of all inner fractions. The inner denominators are (x7)(x-7), (x+7)(x+7), and x249x^2-49. Recognize that x249x^2-49 is a difference of squares: x249=(x7)(x+7)x^2-49 = (x-7)(x+7). Since this already contains the other two denominators as factors, the LCD is (x7)(x+7)(x-7)(x+7).

Step 2. Multiply the numerator and denominator by the LCD, (x7)(x+7)(x-7)(x+7). (x7)(x+7)2x7(x7)(x+7)1x+7(x7)(x+7)6x+7(x7)(x+7)1(x7)(x+7)\frac{(x-7)(x+7) \cdot \frac{2}{x-7} - (x-7)(x+7) \cdot \frac{1}{x+7}}{(x-7)(x+7) \cdot \frac{6}{x+7} - (x-7)(x+7) \cdot \frac{1}{(x-7)(x+7)}}

Step 3. Simplify by canceling common factors in each term. 2(x+7)1(x7)6(x7)1\frac{2(x+7) - 1(x-7)}{6(x-7) - 1}

Step 4. Distribute and combine like terms in the numerator and denominator. Numerator: 2x+14x+7=x+212x + 14 - x + 7 = x + 21 Denominator: 6x421=6x436x - 42 - 1 = 6x - 43

The simplified expression is x+216x43\frac{x + 21}{6x - 43}.

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Updated 2026-04-30

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