How do you factor completely: 15b^2-36b-96?

Jul 16, 2015

Factor: f(b) = 15b^2 - 36b - 96
Answer: f(b) = 3(5b + 8)(b - 4)

Explanation:

f(b) = 3y = 3(5b^2 - 12b - 32). Factor y.
I use the new AC Method (Google, Yahoo Search)
Converted y' = b^2 - 12b - 160. p' and q' have opposite signs.
Factor pairs of -160 -->...(-5, 32)(-8, 20). This sum is 12 = -b.
Then p' = 8 and q' = - 20.
p = 8/5 and q = -20/5 = -4

f(b) = 3(5)(b + 8/5)(b - 4) = 3(5b + 8)(b - 4)