已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值.已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值
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已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值.已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值
已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值.
已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值
已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值.已知(x+y)²=7,(x-y)²=3,求x²+y²与xy的值
解
(x+y)²=7
∴x²+2xy+y²=7 ①
(x-y)²=3
∴x²-2xy+y²=3 ②
①+②得:
2x²+2y²=10
∴x²+y²=5
①-②得:
4xy=4
xy=1