x^2-3x-4y^+6y=(x-2y)(x+2y-3)
(x-y)^2-4(x-y-1) =(x-y-2)²
2(a^2-3bc)+a(4b-3c) =(a+2b)(2a-3c)
a^4+a^2b^2+b^4=(a²+ab+b²)(a²-ab+b²)