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How do we factor trinomials?

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Example of Factoring a Trinomial
Factor x2 + 5x + 4
1) identify a,b, and c in the trinomial
ax2 + bx+c a= 1
b= 5
c= 4
2) write down all factor pairs of 4

(Note: since 5 is positive we only need to think about pairs that are either both positive or both negative. Remember a negative times a negative is a positve. As the chart on the right shows you -2*-2 is positive we do have to consider these two negative factors. This is probabily easier to understand if you watch our video lesson factoring trinonmials)
3) identify which factor pair from the previous step sums up to c
4) Substitute that factor pair into two binomials (x +4)(x+1)
5) If you'd like, you can check your work by multiplying the two binomials and verify that you get the original trinomial (x +4)(x+1) = x2 + 5x + 4