Example

Factoring q22q15q^2 - 2q - 15

Factor q22q15q^2 - 2q - 15 by applying the trinomial factoring strategy. The constant term 15-15 is negative, so the two numbers must have opposite signs — one positive and one negative. We need factors of 15-15 whose sum is 2-2.

Step 1 — Set up two binomials with first terms qq: (q)(q)(q\quad)(q\quad).

Step 2 — Find two numbers with opposite signs that multiply to 15-15 and add to 2-2. List all factor pairs of 15-15 and check their sums:

Factors of 15-15Sum of factors
1,151, -151+(15)=141 + (-15) = -14
1,15-1, 151+15=14-1 + 15 = 14
3,53, -53+(5)=23 + (-5) = -2
3,5-3, 53+5=2-3 + 5 = 2

The pair 33 and 5-5 has a product of 15-15 and a sum of 2-2.

Step 3 — Use 33 and 5-5 as the last terms of the binomials: (q+3)(q5)(q + 3)(q - 5).

Step 4 — Check by multiplying: (q+3)(q5)=q25q+3q15=q22q15(q + 3)(q - 5) = q^2 - 5q + 3q - 15 = q^2 - 2q - 15 ✓.

The factored form is (q+3)(q5)(q + 3)(q - 5). This example demonstrates a case where cc is negative and the constant has multiple factor pairs to consider. All four sign arrangements of the factor pairs of 15-15 must be tested — only the pair 33 and 5-5 produces the required sum of 2-2.

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Updated 2026-04-21

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