已知(x+y)^2=11,(x-y)^2=7,求x^2+y^2及xy的值
3个回答
(x+y)^2+(x-y)^2=2x^2+2y^2=18
x^2+y^2=9
(x+y)^2-(x-y)^2=4xy=11-7=4
xy=1
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