求和Sn=1²－2²＋3²－4²……﹙﹣1﹚的n－2次方×n²
求和Sn=1²－2²＋3²－4²……﹙﹣1﹚的n－2次方×n²
数学人气：843 ℃时间：2019-12-01 13:40:00
优质解答
当n为偶数时：1²－2²＋3²－4²……﹙﹣1﹚的n+1次方×n²= (1+2)(1-2) + (3+4)(3-4) + (5+6)(5-6) + .+ (n-1+n)(n-1-n)= -(1+2+3+.+n)= -n(n+1)/2当n为奇数时：1²－2²＋3²－4...
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