4(x-2y)^2-9（2x-y）^2
=[2(x-2y)-3（2x-y)][2(x-2y)+3（2x-y)]
=(2x-4y-6x+3y)(2x-4y+6x-3y)
=(-4x-y)(8x-7y)
=-(4x+y)(8x-7y)