Example

Try It 7.57: Simplifying 1a+1bab+ba\frac{\frac{1}{a}+\frac{1}{b}}{\frac{a}{b}+\frac{b}{a}} Using the LCD

To simplify the complex rational expression 1a+1bab+ba\frac{\frac{1}{a}+\frac{1}{b}}{\frac{a}{b}+\frac{b}{a}} using the least common denominator (LCD) method:

Step 1. Find the LCD of all inner fractions. The denominators are aa, bb, bb, and aa. The LCD is abab.

Step 2. Multiply the numerator and denominator by the LCD, abab.

ab1a+ab1babab+abba\frac{ab \cdot \frac{1}{a} + ab \cdot \frac{1}{b}}{ab \cdot \frac{a}{b} + ab \cdot \frac{b}{a}}

Step 3. Simplify by distributing and canceling common factors in each term:

b+aaa+bb\frac{b + a}{a \cdot a + b \cdot b}

Step 4. Combine terms to obtain the final simplified expression:

b+aa2+b2\frac{b + a}{a^2 + b^2}

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Updated 2026-04-30

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Ch.7 Rational Expressions and Functions - Intermediate Algebra @ OpenStax

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