(x-y)(x+xy+y)+xy(y-x) 其中x=7.1 y=2.92x+y=0,2x-y=0.5,求2x^2-1/2y^2

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(x-y)(x+xy+y)+xy(y-x) 其中x=7.1 y=2.92x+y=0,2x-y=0.5,求2x^2-1/2y^2
(x-y)(x+xy+y)+xy(y-x) 其中x=7.1 y=2.9
2x+y=0,2x-y=0.5,求2x^2-1/2y^2

(x-y)(x+xy+y)+xy(y-x) 其中x=7.1 y=2.92x+y=0,2x-y=0.5,求2x^2-1/2y^2
1.
(x-y)(x+xy+y)+xy(y-x)
=(x-y)(x+xy+y-xy)
=(x-y)(x+y)
=(7.1-2.9)*(7.1+2.9)
=10*4.2
=42
2.
2x+y=0 (1)
2x-y=0.5 (2)
(1)+(2)得：
4x=0.5
x=0.125=1/8
y=-0.25=-1/4
2x²-y²/2
=1/32-1/32
=0

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