(x²+3y)(x-2y)-(y+2x)(2x-y)
=x³-2x²y+3xy-6y²-4x²+y²
=x³-4x²-2x²y+3xy-5y²不好意思，打错了是(2x+3y)(x-2y)-(y+2x)(2x-y)(2x+3y)(x-2y)-(y+2x)(2x-y)=2x²-xy-6y²-4x²+y²=-2x²-xy-5y²