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把$x_1x_2+x_2x_3+\cdot+x_{n-1}x_n$化为标准型

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其妙 posted 2014-6-25 15:54 |Read mode

作变换把$x_1x_2+x_2x_3+\cdot+x_{n-1}x_n$化为标准型
（即化为若干平方之和或者之差，例如$y_1^2-y_2^2+y_3^2-y_4^2+\cdots+$之类的）

妙不可言，不明其妙，不着一字，各释其妙！

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kuing posted 2014-6-25 16:42

$4xy=(x+y)^2-(x-y)^2$ 不就行了

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original poster 其妙 posted 2014-6-25 19:40

回复 2# kuing

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