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Example

Showing 2x2+6x+52x^2 + 6x + 5 Is a Prime Trinomial

Attempt to factor 2x2+6x+52x^2 + 6x + 5 by applying the ac method for trinomials with a leading coefficient other than 1.

Step 1 — Check for a GCF. The terms 2x22x^2, 6x6x, and 55 share no common factor, so proceed.

Step 2 — Find the product aca \cdot c. Here a=2a = 2 and c=5c = 5, so ac=2(5)=10a \cdot c = 2(5) = 10.

Step 3 — Find two numbers that multiply to 10 and add to 6. List all factor pairs of 10 and check their sums:

Factors of 1010Sum of factors
1,101, 101+10=111 + 10 = 11
2,52, 52+5=72 + 5 = 7

Neither factor pair produces a sum of 6.

Since no pair of integers has a product of 10 and a sum of 6, the trinomial 2x2+6x+52x^2 + 6x + 5 cannot be factored — it is a prime polynomial. This example extends the concept of prime trinomials to expressions of the form ax2+bx+cax^2 + bx + c where a1a \neq 1: instead of looking for factor pairs of the constant term cc, the ac method requires factor pairs of the product acac. When no such pair has the correct sum, the trinomial is prime regardless of whether the leading coefficient is 1 or not.

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Updated 2026-04-21

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