1. Factoring Polynomials NCVPS Summer 2010

2. Factoring is reversing the process of multiplying monomials, binomials or trinomials or any combination of these. We will focus on factoring out monomials (we call these GCFs) from a polynomial or factoring trinomials into two binomials. Ex: 3x(a – 3) or (x – 1)(x + 5) | | / monomial binomial binomials What is factoring?

3. Sometimes a common factor is present. Ex 1: 3x2 – 6x -9 has a common factor of 3: 3(x2 – 2x – 3) Ex 2: x3-5x2+4x has a common x in all 3 terms: x(x2 - 5x + 4) Ex 3: 2x2a + 6xa+12a has a common factor of 2a: 2a(x2 + 3x + 6) Step 1: Look for a GCF present

4. Factor first term into its products. Example 1: x2– 2x – 3. The first term is x2. It is factored as x*x. Factor the last term into its products. The last term is -3. It factors as 1(-3) or (-1)(3) Step 2: Factor first & last terms

5. Example 1: x2 – 2x – 3. (x )(x ) Next, add the factors of -3: x2– 2x – 3 (x -3)(x +1) Example 1 continued

6. It is very important to check your factoring to make sure you got the signs in the correct place. Multiply them out again! x2 - 2x – 3 = (x -3)(x +1) F: x(x) O: (-3)(1) = -3 I: -3x L: 1x Inner + Last terms = -2x Check the work!

7. Checking the signs is very important! x2 + 3x + 2 has all + signs. It factors with + signs: (x + 2)(x + 1) x2 – 6x + 5 has a +5 but the middle term is -. So 5 must factor as (-5)(-1): (x - 5)(x – 1) More examples on the next page  Signs, signs, everywhere there’s signs!

8. X2 -2x – 8 has a -8 that factors as + and – Here we work with factors and sums. We want a sum of the factors to be -2 (the middle term) (-8)(1) = -8 sum the factors: -8+1 = -7 (8)(-1) = -8 sum the factors: 8 + (-1) = 7 (-4)(2) = -8 sum the factors: -4 + 2 = -2 This last one is the factorization we want! (x – 4)(x + 2) Keep on checking signs!

9. Find the factorization of x2 – 4x -12 -12 factors as (-3)(4) or (3)(-4) or (2)(-6) or (-2)(6) or (-1)(12) or (1)(-12). Which of these sums to -4? -3 + 4 = 1 3 + (-4) = -1 2 + (-6) = -4 We have a winner! x2 -4x – 12 is (x + 2)(x – 6) Another example

10. x2 – 2x – 15 2x2 – x – 3 3x2-12x +9 Go to the next slide for the solutions. You Try Problems

11. x2 – 2x – 15 = (x – 5)(x + 3) 2x2 – x – 3 = (2x - 3)(x +1) 3x2-12x +9 = 3(x2 – 4x + 3) = 3(x – 3)(x -1) You Try Problems