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1x2+2x3+3x4+...+nx(n+1)= 1x2x3+2x3x4+...+n(n+1)(n+2)= 只写答案
人气:411 ℃ 时间:2019-08-21 16:41:40
解答
1x2+2x3+3x4+...+nx(n+1) = n(n+1)(n+2) /3
1x2x3+2x3x4+...+n(n+1)(n+2) = n(n+1)(n+2)(n+3) /4
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