已知x+y=3,4xy=3.求（x-y）ˇ2的值
人气：182 ℃ 时间：2020-02-06 03:17:53
解答
(x-y)^2
=x^2-2xy+y^2
=x^2+2xy+y^2-4xy
=(x+y)^2-4xy
=3^2-3
=9-3=6-4xy从哪里来的？我晕哦，-2xy=-4xy+2xy
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