Example

Factoring 14x247x714x^2 - 47x - 7

Factor 14x247x714x^2 - 47x - 7 completely using the trial and error method. This trinomial has a negative last term and a leading coefficient with multiple factor pairs, producing the largest number of combinations seen so far.

Step 1 — Write in descending order. The trinomial 14x247x714x^2 - 47x - 7 is already in descending order.

Step 2 — Find factor pairs of the first term. The term 14x214x^2 can be factored into first-degree terms in two ways: x14xx \cdot 14x or 2x7x2x \cdot 7x.

Step 3 — Find factor pairs of the last term and consider signs. The last term 7-7 is negative, so its two factors must have opposite signs — one positive and one negative. The factor pairs are 1,71, -7 and 1,7-1, 7.

Step 4 — Test all combinations. Each pair of factors of 14x214x^2 is combined with each pair of factors of 7-7, and the order within each pair matters, producing eight trial factorizations. However, four of these can be eliminated immediately using the GCF shortcut: since the original trinomial has no common factor, any trial binomial whose terms share a common factor is impossible. For example, (x+1)(14x7)(x + 1)(14x - 7) is not an option because 14x14x and 7-7 share a factor of 7. After eliminating these invalid combinations, only four remain:

Possible factorsProduct
(x7)(14x+1)(x - 7)(14x + 1)14x297x714x^2 - 97x - 7
(x+7)(14x1)(x + 7)(14x - 1)14x2+97x714x^2 + 97x - 7
(2x7)(7x+1)(2x - 7)(7x + 1)14x247x714x^2 - 47x - 7
(2x+7)(7x1)(2x + 7)(7x - 1)14x2+47x714x^2 + 47x - 7

The combination (2x7)(7x+1)(2x - 7)(7x + 1) produces the correct middle term 47x-47x.

Step 5 — Check by multiplying: (2x7)(7x+1)=14x2+2x49x7=14x247x7(2x - 7)(7x + 1) = 14x^2 + 2x - 49x - 7 = 14x^2 - 47x - 7

The factored form is (2x7)(7x+1)(2x - 7)(7x + 1). This example is the first where the constant term is negative in a trinomial of the form ax2+bx+cax^2 + bx + c with a1a \neq 1. A negative constant means the last-term factors must have opposite signs, which doubles the number of sign arrangements compared to a positive constant. It also demonstrates how the GCF elimination shortcut cuts the work in half — reducing eight trial factorizations to just four that need to be tested.

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Updated 2026-04-21

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