Example

Adding 7x+12x+3+x2x+3\frac{7x+12}{x+3} + \frac{x^2}{x+3}

Add two rational expressions that share the denominator x+3x + 3, then factor and simplify: 7x+12x+3+x2x+3\frac{7x + 12}{x + 3} + \frac{x^2}{x + 3} Step 1 — Add the numerators over the common denominator. Since both fractions share x+3x + 3 as their denominator, combine the numerators: 7x+12+x2x+3\frac{7x + 12 + x^2}{x + 3}. Rearranging the numerator into standard form (descending degree order) gives: x2+7x+12x+3\frac{x^2 + 7x + 12}{x + 3} Step 2 — Factor the numerator and denominator completely. The trinomial x2+7x+12x^2 + 7x + 12 factors as (x+3)(x+4)(x + 3)(x + 4), since 3+4=73 + 4 = 7 and 34=123 \cdot 4 = 12. The denominator x+3x + 3 cannot be factored further: (x+3)(x+4)x+3\frac{(x + 3)(x + 4)}{x + 3} Step 3 — Simplify by dividing out the common factor. Cancel the shared factor x+3x + 3 from the numerator and denominator: x+4x + 4. This example demonstrates the three-step rational expression addition procedure in action: combining numerators, factoring the resulting polynomial completely, and canceling the common factor. Unlike simpler cases where the combined numerator cannot be factored, here the trinomial numerator shares a binomial factor with the denominator, reducing the expression to a simple binomial.

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Updated 2026-06-25

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

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