(x+y)²=1 (x-y)²=49 求x²+y²与xy的值
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![(x+y)²=1 (x-y)²=49 求x²+y²与xy的值](/uploads/image/z/1014609-57-9.jpg?t=%28x%EF%BC%8By%29%26%23178%3B%EF%BC%9D1+%28x%EF%BC%8Dy%29%26%23178%3B%3D49+%E6%B1%82x%26%23178%3B%EF%BC%8By%26%23178%3B%E4%B8%8Exy%E7%9A%84%E5%80%BC)
(x+y)²=1 (x-y)²=49 求x²+y²与xy的值
(x+y)²=1 (x-y)²=49 求x²+y²与xy的值
(x+y)²=1 (x-y)²=49 求x²+y²与xy的值
(x+y)²=1 x²+2xy+y²=1 ①
(x-y)²=49 x²-2xy+y² =49 ②
①+② 2(x²+y²) =50
x²+y² =25
带入① 2xy=-24
xy=-12