I've been trying this alooot of times and couldn't get this answer in the book : 4(x-1)(2x+1)
This is the problem: 9x^2-(x+2)^2
1. Difference of two squares.
(3x-(x+2)(3x+(x+2))=
(2x-2)(4x+2)
take 2 out of each parenthesis.
2(x-1)(2(2x+1)
4(x-1)(2x+1)