已知（x+y)^2=64,(x-y)^2=4,求xy以及x^2+y^2.

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已知（x+y)^2=64,(x-y)^2=4,求xy以及x^2+y^2.
已知（x+y)^2=64,(x-y)^2=4,求xy以及x^2+y^2.

已知（x+y)^2=64,(x-y)^2=4,求xy以及x^2+y^2.
（x+y)^2=64
(x-y)^2=4
两式相减得 4xy=60
2xy=30
xy=15
x^2+y^2=（x+y)^2-2xy=64-30=34

（x+y)^2-(x-y)^2=4xy=60 所以=15
x^2+y^2=（x+y)^2-2xy=34

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