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x+y=3,xy=1,x^2+y^2=?
人气:443 ℃ 时间:2020-05-10 19:41:15
解答
x^2+y^2
=x^2+y^2+2xy-2xy
=(x+y)²-2xy
=(3)²-2×1
=9-2
=7
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