Example

Subtracting 4a2+6a+53a2+7a+10\frac{4}{a^2+6a+5} - \frac{3}{a^2+7a+10}

Subtract two rational expressions with different factorable trinomial denominators:

4a2+6a+53a2+7a+10\frac{4}{a^2 + 6a + 5} - \frac{3}{a^2 + 7a + 10}

Step 1 — Factor the denominators to find the LCD. Factor each trinomial: a2+6a+5=(a+1)(a+5)a^2 + 6a + 5 = (a + 1)(a + 5) a2+7a+10=(a+5)(a+2)a^2 + 7a + 10 = (a + 5)(a + 2) The LCD is (a+1)(a+5)(a+2)(a + 1)(a + 5)(a + 2).

Step 2 — Rewrite each fraction with the LCD. The first fraction is missing the factor (a+2)(a + 2); the second is missing (a+1)(a + 1): 4(a+2)(a+1)(a+5)(a+2)3(a+1)(a+5)(a+2)(a+1)\frac{4(a + 2)}{(a + 1)(a + 5)(a + 2)} - \frac{3(a + 1)}{(a + 5)(a + 2)(a + 1)}

Distribute in the numerators: 4a+8(a+1)(a+5)(a+2)3a+3(a+1)(a+5)(a+2)\frac{4a + 8}{(a + 1)(a + 5)(a + 2)} - \frac{3a + 3}{(a + 1)(a + 5)(a + 2)}

Step 3 — Subtract the numerators. Subtract the second numerator from the first over the common denominator, distributing the negative sign to both terms in (3a+3)(3a + 3): 4a+8(3a+3)(a+1)(a+5)(a+2)\frac{4a + 8 - (3a + 3)}{(a + 1)(a + 5)(a + 2)}

4a+83a3(a+1)(a+5)(a+2)\frac{4a + 8 - 3a - 3}{(a + 1)(a + 5)(a + 2)}

Combine like terms: a+5(a+1)(a+5)(a+2)\frac{a + 5}{(a + 1)(a + 5)(a + 2)}

Step 4 — Simplify by removing common factors. The factor (a+5)(a + 5) appears in both the numerator and the denominator. Cancel it: 1(a+1)(a+2)\frac{1}{(a + 1)(a + 2)}

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Updated 2026-04-30

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