求和Sn=1²-2²+3²-4²……﹙﹣1﹚的n-2次方×n²
人气:380 ℃ 时间:2019-12-01 13:40:00
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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