(a-3)²+a-3=(a-3)(a-3+1)=(a-3)(a-2)
(x+y)²+x+y=(x+y)(x+y+1)
(2b-1)²- (b +2)²=
=(2b-1+b+2)(2b-1-b-2)=
=(3b+1)(b-3)