2x^2+xy-y^2-4x+5y-6=(2x-y)(x+y)-4x+5y-6=(2x-y)(x+y)+(2x+2y)-6x+3y-6=(2x-y)(x+y)+2(x+y)-6x+3y-6=(x+y)(2x-y+2)-3(2x-y+2)=(x+y-3)(2x-y+2)所以x+y-3=0或者2x-y+2=0y=x-3或者y=2x+22条直线
