SOLUTION: I need to factor these by trial and error... do you think you can show step by step and explain a little plz.... (A) 18x^2-11x-24 (B) 40x^2+7x-20

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: I need to factor these by trial and error... do you think you can show step by step and explain a little plz.... (A) 18x^2-11x-24 (B) 40x^2+7x-20      Log On


   

Question 438539: I need to factor these by trial and error... do you think you can show step by step and explain a little plz....
(A) 18x^2-11x-24 (B) 40x^2+7x-20
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
I believe this technique is called the "British" method (maybe it is primarily taught there)

(A) multiply the first and last terms ___ (18x^2)(-24) = -432x^2
___ factor -432x^2 so that the sum of the factors will be the middle term (-11x) ___ (-27x) + (16x) = -11x
___ use the factors for a grouping solution ___ (18x^2 - 27x) + (16x - 24) ___ [9x(2x - 3)] + [8(2x - 3)]

(9x + 8)(2x - 3)