1.ax-ay-x+y
=a(x-y)-(x-y)
=(a-1)(x-y)
2.2b(x+y)-x-y
=2b(x+y)-(x+y)
=(x+y)(2b-1)
3.x^2-5x-6+mx+m
=(x-6)(x+1)+m(x+1)
=(x+1(x-6+m)
4.a^2-6ab+9b^2-4
=(a-3b)^2-2^2
=(a-3b+2)(a-3b-2)
5.9-a^2-4ab-4b^2
6.1+a^2b^2-a^2-b^2
=(a^2+2ab+1)-(a^2+2ab+b^2)
=(ab+1)^2-(a+b)^2
=(ab+1+a+b)(ab+1-a-b)
=[a(b+1)+(b+1)][a(b-1)-(b-1)]
=(b+1)(a+1)(a-1)(b-1)