SOLUTION: I need help factoring these polynomials completely. 20x squared - 7x - 6 ab - a - b + 1 and -8z squared + 48z

SOLUTION: I need help factoring these polynomials completely. 20x squared - 7x - 6 ab - a - b + 1 and -8z squared + 48z - 72

Question 115795: I need help factoring these polynomials completely.
20x squared - 7x - 6
ab - a - b + 1
and -8z squared + 48z - 72
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
20x^2 - 7x - 6
20*-6=-120 multiply 1st and last coefficients.
find 2 factors of -120 whose sum is -7. Ans: -15, +8 The rest is easy.
(20x^2-15x)+(8x-6) factoring by grouping.
5x(4x-3)+2(4x-3)
(5x+2)(4x-3) It works every time!
.
-8z^2 + 48z - 72
-8*-72=576 Wow, this is humongous.
Find the 2 factors of 576 that add up to 48. Ans 24, 24 It took a while.
(-8z^2+24z)+(24z-72)
-8z(z-3)+24(z-3)
(-8z+24)(z-3)
-(8z-24)(z-3)
.
ab - a - b + 1 This one is so easy that I know you are chomping at the bit to do it yourself.
a(b-1)-(b-1) factoring by grouping again.
(a-1)(b-1)
.
Ed

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