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已知x-xy=20,xy-y=-10,则x-y=?,x+y-2xy?
人气:191 ℃ 时间:2020-05-14 00:28:40
解答
X-Y=X-XY+XY-Y
=20-10
=10
X+Y-2XY
=X-XY-(XY-Y)
=20-(-10)
=30
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