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(3x-y)²-(2x+y)²+5y²
人气:148 ℃ 时间:2020-01-14 14:34:41
解答
(3x-y)^2-(2x+y)^2+5y^2
=9x^2-6xy+y^2-4x^2-4xy-y^2+5y^2
=5x^2-10xy+5y^2
=5(x^2-2xy+y^2)
=5(x-y)^2
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