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Factoring Trinomials, a is not 1 - Problem 2 6,561 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

Here I have a trinomial where the leading coefficient I not 1 and I’m asked to factor it. That makes me kind of bummed out because I know it's not going to be easy. This is also like double not easy because my leading coefficient has more than one set of factor pairs.

Like I don't know if I’m going to be working with 6x and x and then some kind of things that multiply to 5 or maybe it will be like this 2x and 3x all I know is that these first terms need to multiply to 6x² and the last terms need to multiply to 5.

It’s going to involve some guessing and checking using Foil. So I’m just going to guess this guy numbers that multiply to 5 have to be 5 and 1 so that's good. Let me try sticking them here I’m just guessing where they might go or let's check, let's use Foil.

Firsts 6x² outers I’ll have 6x inners is 5x, shoot I already know it’s not right because I needed them to add up to 17. That's only 11x. I'm just going to guess again let's try this one, I’m going to guess where to put 5 and 1.

Some of you guys probably just saw me look at my paper just now I’ll tell you I already did this problem so I know. I did some guessing and checking before I came in to show you this video. And that is just what happens like even though I’m a Math teacher I still need to use guess and check in order to solve these problems.

I know this one is going to be correct because when I Foil I get 2x plus 15x and that gives me my 17x middle term. That's how I know it’s correct by Foiling. So again you guys you get better with practice but even me like I’m a Math teacher I have to do guess and check I get them wrong a lot of the times and I just go through and keep starting all over again.

Get a pencil so you can erase and make sure you get these problems correct. The way you’ll know they’re correct is when you foil you should get the original trinomial.

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