先化简,再求值(x-2y)(x+3y)-(2x-y)(x-4y)其中x=-1y=2_数学解答

先化简,再求值(x-2y)(x+3y)-(2x-y)(x-4y)其中x=-1y=2

人气：438 ℃　时间：2019-08-20 01:04:43

解答

(x-2y)(x+3y)-(2x-y)(x-4y)=x²+3xy-2xy-6y²-(2x²-8xy-xy+4y²)=x²+3xy-2xy-6y²-2x²+9xy-4y²=-x²+10xy-10y²=-1-20-40=-61