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Factoring Trinomials, a is not 1 - Concept

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

Long division can be used to divide a polynomial by another polynomial, in this case a binomial of lower degree. When dividing polynomials, we set up the problem the same way as any long division problem, but are careful of terms with zero coefficients. For example, in the polynomial x^3 + 3x + 1, x^2 has a coefficient of zero and needs to be included as x^3+ 0x^2+3x+1in the division problem.

Here I'm given a trinomial with a leading coefficient is 1 but I have something that's little tricky here, I have a minus sign so when I'm asked to factor this, this tells me the product of two numbers gives me the answer -10.
If you have two numbers and the answer is negative that means one of your numbers has to be a negative value. I'm going to keep that in mind when I'm looking for things that multiplied a negative 10 and add up to positive 3, so numbers that multiply to 10 might be a pair of 1 and 10 or 2 and 5 and that's it those are the only pairs so it's going to be some combination of these with some pluses and minuses one has to be negative one has to positive so that when I add them up the answer is positive 3. A lot of you guys can do that pretty quickly notice that if I were to use positive 5 and -2 the products will be -10 and the sum will be +3, so there's my factors p take away 2 and p+5 that's the factored form of this trinomial. Check you work by foiling just to make sure first, outers, inners, last combine these and you'll see that we did do it correctly we have 3p as the middle term there and we know we did it right. So what I want to leave you with is if you see a negative sign before you c term that means one of your numbers that go into your factor is going to be negative the other one is going to be positive, so you want to keep that in mind when you're looking at your factor pairs for the c term.

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