先化简再求值2(x+y)-(2x-y)(x-y),其中x=1,y=-1
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2(x+y)-(2x-y)(x-y)
=2(x+y)-(x+x-y)(x-y)
=2(x+y)-x(x-y)-(x-y)^2
x+y=0
x-y=2
则 2(x+y)-(2x-y)(x-y)=2(x+y)-x(x-y)-(x-y)^2
=-2-4
=-6
=2(x+y)-(x+x-y)(x-y)
=2(x+y)-x(x-y)-(x-y)^2
x+y=0
x-y=2
则 2(x+y)-(2x-y)(x-y)=2(x+y)-x(x-y)-(x-y)^2
=-2-4
=-6
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