若(x+y)2=36,(x-y)2=16,求xy与x2+y2的值.
人气:226 ℃ 时间:2020-05-27 11:43:04
解答
∵(x+y)2=36,(x-y)2=16,
∴x2+2xy+y2=36,①
x2-2xy+y2=16,②
①-②得4xy=20,
∴xy=5,
①+②得2(x2+y2)=52,
∴x2+y2=26.
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