2(x^2y+xy)-3(x^2y-xy)-4x^2y
=2x^2y+2xy-3x^2y+3xy-4x^2y
=-5x^2y+5xy
x=1，y=-1
=-5*1*(-1)+5(-1)*1
=5-5=0
~望采纳
2(x²y+xy)-3(x²y-xy)-4x²y
=2x²y+2xy-3x²y+3xy-4x²y
=2x²y-3x²y-4x²y+2xy+3xy
=-5x²y+5xy
=-5xy(x-1)
=-5*1*(-1)*(1-1)
=0
2（x的2次方乘y+xy)-3(x的2次方乘y-xy)-4x的 2次方乘y
=2x的2次方•y+2xy-3x的2次方y+3xy-4x的2次方乘y
=-5x的2次方乘y+5xy
x=1, y=-1时，
原式=5-5=0。
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