已知(x+y)²=11,(x-y)²=9,则xy= .
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![已知(x+y)²=11,(x-y)²=9,则xy= .](/uploads/image/z/7161102-54-2.jpg?t=%E5%B7%B2%E7%9F%A5%EF%BC%88x%2By%EF%BC%89%26%23178%3B%3D11%2C%EF%BC%88x-y%EF%BC%89%26%23178%3B%3D9%2C%E5%88%99xy%3D+.)
已知(x+y)²=11,(x-y)²=9,则xy= .
已知(x+y)²=11,(x-y)²=9,则xy= .
已知(x+y)²=11,(x-y)²=9,则xy= .
(x+y)²=11,(x-y)²=9,
x^2+2xy+y^2=11
x^2-2xy+y^2=9
相减4xy=2
xy=1/2
(x+y)²-(x-y)²=11-9
4xy=2
xy=1/2
4xy=(x+y)²-(x-y)²=11²-9²=121-81=40
所以xy=10