作业帮x-xy=40,xy-y= -20,求代数式x-y和x+y-2xy算试
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x-xy=40,xy-y= -20,求代数式x-y和x+y-2xy算试
x-xy=40,xy-y= -20,求代数式x-y和x+y-2xy
算试
x-xy=40,xy-y= -20,求代数式x-y和x+y-2xy算试
(x-xy)+(xy-y)=40-20
x-xy+xy-y=20
x-y=20
(x-xy)-(xy-y)=40-(-20)
x-xy-xy+y=60
x+y-2xy=60
X-XY=4O
XY-Y=-20
1.
XY=X-40
X-40-Y=-20
X-Y=20
2.
前式+后式:X-Y=20,前式-后式:X+Y-2XY=60...
...
x-y=(x-xy)+(xy-y)=40+(-20)=20
x+y-2xy=(x-xy)-(xy-y)=40-(-20)=60
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