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}

Step 2 — Rearrange the numerator in standard form (descending degree order):

x2+7x+12x+3\frac{x^2 + 7x + 12}{x + 3}

Step 3 — Factor the numerator. 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:

(x+3)(x+4)x+3\frac{(x + 3)(x + 4)}{x + 3}

Step 4 — Simplify by dividing out the common factor. Cancel the shared factor (x+3)(x + 3) from the numerator and denominator:

x+4x + 4

This example demonstrates all three steps of the rational expression addition procedure in action: combining numerators, factoring the resulting polynomial completely, and canceling the common factor with the denominator. Unlike the simpler case 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 2026-04-21

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