x^2+xy-6y^2-6x+2y+8
=(x-2y)(x+3y)-(2x+6y)-(4x-8y-8)
=(x-2y)(x+3y)-2(x+3y)-4(x-2y-2)
=(x+3y)(x-2y-2)-4(x-2y-2)
=(x-2y-2)(x+3y-4)