1x1-2x2+3x3-4x4+5x5-6x6......-100x100+101x101

简便算法答案

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原式
=1+5+9+13。。。+201
=（201+1）x21÷2
=5151

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=101+100+99+……+3+2+1
两两拆分，用平方差公式就行了

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