2x3/1+3x4/1+4x5/1.41x42/1的和
<p>问题：2x3/1+3x4/1+4x5/1.41x42/1的和<p>答案：↓↓↓<p class="nav-title mt10" style="border-top:1px solid #ccc;padding-top: 10px;">陈丽亚的回答：<div class="content-b">网友采纳 an=(n+1)(n+2)=(n+1)^2+(n+1) 原式=Sn=2^2+3^2+……+41^2+2+3+……+41 =41*42(82+1)/6-1+40(2+41)/2 =23821-1+860=24680
页:
[1]