若xx+yy=2,x+y=1则xy=?

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若xx+yy=2,x+y=1则xy=?若xx+yy=2,x+y=1则xy=?若xx+yy=2,x+y=1则xy=?(x+y)(x+y)=1,展开,得xx+2xy+yy=1,代入,得2+2xy=1,得x

若xx+yy=2,x+y=1则xy=?
若xx+yy=2,x+y=1则xy=?

若xx+yy=2,x+y=1则xy=?
(x+y)(x+y)=1,展开,得xx+2xy+yy=1,代入,得2+2xy=1,得xy=-0.5

-1/2

....这个问题挺可爱的啊..*_*
xx+yy =2
x+y=1
So:
(x+y)*(x+y)-(xx+yy)=2xy.
然后就可以知道xy了啊...
-0.5

(x+y)的平方=x的平方+y的平方+2xy=1
得xy=-1/2

-1/2

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