初一数学：4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]其中x=2,y=－1
问题描述：
初一数学：4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]其中x=2,y=－1
答
4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]
=4xy-(x^2+5xy-y^2-x^2-3xy+2y^2)
=4xy-(2xy+y^2)
=4xy-2xy-y^2
=2xy-y^2
=y(2x-y)
=(-1)(2*2+1)
=-5