so factor
use reverse distributiver property
ab+ac=a(b+c) or
ab-ac=a(b-c)
so we need to find a
find the common factors of the variables
4=2 times 2
8=2 times 2 times 2
common is 2 times 2=4
so 4 is a factor of both
so
4x-8=(4)x-(4)2=(4)(x-2)
4(x-2) is the answer
