4x^2-4x-y^2+4y-3
=4x^2-4x-y^2+4y+1-4
=4x^2-4x+1-y^2+4y-4
=(2x-1)^2-(y^2-4y+4)
=(2x-1)^2-(y-2)^2
=(2x-1+y-2)(2x-1-y+2)
=(2x+y-3)(2x-y+1)