2x^2+xy-y^2-4x+5y-6
=（x+y）(2x-y)-4x+5y-6
=（x+y）(2x-y)+2(x+y)-6x+3y-6
=(x+y)(2x-y+2)-3(2x-y+2)
=(2x-y+2)(x+y-3)