已知xy=8,满足x²y-Xy²-x+y=56,求x²+y²的值.
人气：152 ℃ 时间：2019-10-24 10:01:52
解答
x²y-Xy²-x+y=56
xy(x-y)-(x-y)=56
(x-y)(xy-1)=56
因为 xy=8
所以 x-y=56/(xy-1)=56÷7=8
x²+y²=(x-y)²+2xy=8²+2×8=80
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