原式=(21x²-14xy-7x-6xy+4y²+2y)-(36x²+24xy+27xy+18y²)
=21x²-20xy-7x+4y²+2y-36x²-51xy-18y²
=-15x²-71xy-14y²-7x+2y请摄入x=2y=1自己做吧
采纳吧你做的和我的答案不一样啊