Example

Adding 2a2ab+b2+3a4a2b2\frac{2a}{2ab+b^2} + \frac{3a}{4a^2-b^2}

Add two rational expressions whose denominators require different polynomial factoring techniques — GCF extraction and the difference of squares pattern:

2a2ab+b2+3a4a2b2\frac{2a}{2ab + b^2} + \frac{3a}{4a^2 - b^2}

Step 1 — Find the LCD and rewrite each fraction. Factor each denominator completely. Extract the GCF from the first: 2ab+b2=b(2a+b)2ab + b^2 = b(2a + b). Apply the difference of squares pattern to the second: 4a2b2=(2a+b)(2ab)4a^2 - b^2 = (2a + b)(2a - b). Both share the factor (2a+b)(2a + b), so the LCD is b(2a+b)(2ab)b(2a + b)(2a - b).

The first fraction 2ab(2a+b)\frac{2a}{b(2a + b)} is missing the factor (2ab)(2a - b); multiply its numerator and denominator by (2ab)(2a - b):

2a(2ab)b(2a+b)(2ab)\frac{2a(2a - b)}{b(2a + b)(2a - b)}

The second fraction 3a(2a+b)(2ab)\frac{3a}{(2a + b)(2a - b)} is missing the factor bb; multiply its numerator and denominator by bb:

3abb(2a+b)(2ab)\frac{3ab}{b(2a + b)(2a - b)}

Step 2 — Add the numerators over the common denominator. Distribute in each numerator and combine like terms:

4a22ab+3abb(2a+b)(2ab)=4a2+abb(2a+b)(2ab)\frac{4a^2 - 2ab + 3ab}{b(2a + b)(2a - b)} = \frac{4a^2 + ab}{b(2a + b)(2a - b)}

Step 3 — Simplify, if possible. Factor the numerator by extracting its GCF: 4a2+ab=a(4a+b)4a^2 + ab = a(4a + b):

a(4a+b)b(2a+b)(2ab)\frac{a(4a + b)}{b(2a + b)(2a - b)}

The factor aa and the binomial (4a+b)(4a + b) do not match any denominator factor, so the expression is already fully simplified.

This example advances beyond monomial and linear-binomial denominators by combining two polynomial factoring methods — GCF extraction and difference of squares — within a single addition problem. After rewriting each fraction with the LCD, the equivalent fractions must be kept in their unsimplified form until the numerators have been combined; canceling shared factors prematurely would destroy the common denominator.

0

1

Updated 2026-04-21

Contributors are:

Who are from:

Tags

OpenStax

Elementary Algebra @ OpenStax

Ch.8 Rational Expressions and Equations - Elementary Algebra @ OpenStax

Algebra

Math

Prealgebra

Related
Learn After