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Factoring Trinomials, a is not 1 - Problem 3

5,813 views
Teacher/Instructor Alissa Fong
Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

In this trinomial I’m asked to factor and my leading coefficient not only is it not 1 but it’s a negative number. For a lot of students it freaks them out but don't worry, you’ll still use the same process where my first two terms need to multiply to -3.

I'm just going to guess that the negative might attach to the 3 it also might be that I have positive 3x and –x. I don't know this is a guess and check type of problem. Let me start here see if I can find something where my leading terms broke down to -3x and x now I need things that will multiply to -10.

I'm thinking some combination of 5 and 2, 5 and sorry -2 because I need them to have a negative product. Let's see how I did let's check by foiling I have -3x squared outers I’ll have -15x inners minus 2x. Oh! Good you guys look there it is there's that -17x take away 10, sweet! That means I did it correctly. I was lucky on that one I got it right on the first trial.

Sometimes it happens sometimes it doesn't but again you guys these are just guess and check type of problems, figure out things whose product is this figure out things whose product is that and then look for combinations. You are going to have to rearrange and adjust the positive and negative signs so that when you FOIL your middle term is correct.

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