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Showing y26y+15y^2 - 6y + 15 Is a Prime Trinomial

Attempt to factor y26y+15y^2 - 6y + 15 by applying the trinomial factoring strategy. The constant term 1515 is positive and the middle coefficient 6-6 is negative, so both numbers in the factor pair must be negative.

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

Step 2 — Find two negative numbers that multiply to 15 and add to 6-6. List all negative factor pairs of 15 and check their sums:

Factors of 15Sum of factors
1,15-1, -151+(15)=16-1 + (-15) = -16
3,5-3, -53+(5)=8-3 + (-5) = -8

Neither factor pair produces a sum of 6-6.

Since no pair of integers has a product of 1515 and a sum of 6-6, the trinomial y26y+15y^2 - 6y + 15 cannot be factored — it is a prime trinomial. This example illustrates the method for confirming that a trinomial is prime: systematically list every possible factor pair, show that none of them yield the required sum, and conclude that the expression is already in its simplest form.

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Updated 2026-04-21

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