a^2+ab-ac-bc
=a(a+b)-c(a+b)
=(a+b)(a-c)
x^2+2x+1-64y^2
=(x+1)^2-64y^2
=(x+1+8y)(x+1-8y)
x^2-9y^2-3x+9y
=(x+3y)(x-3y)-3(x-3y)
=(x-3y)(x+3y-3)