a精品视频_日韩欧美在线视频一区二区三区_www色网_日本一卡2卡三卡4卡免费网站_欧美韩日一区_国产一级精品绿帽视频_日本欧美在线_精品一区二区三区网站_视频一二三区_欧美一级无毛_国产精品久久久久久爽爽爽_韩国av免费观看_欧美老熟妇乱大交xxxxx_国产成人高清啪免费观看软件_日韩欧美亚洲中文乱码_√8天堂资源地址中文在线_求个毛片网站_黄色网址网站_国产成人午夜不卡在线视频_中文字幕在线无码一区二区三区

1/(n2+n)+ 2/(n2+n)+...+n/(n2+n)<1/(n2+1)+ 2/(n2+2)+...+n/(n2+n)<1/(n2+1)+2/(n2+1)+...+n/(n2+1)(1+2+...+n)/(n2+n)<1/(n2+1)+ 2/(n2+2)+...+n/(n2+n)<(1+2+...+n)/(n2+1)[n(n+1)/2]/(n2+n)<1/(n2+1)+ 2/(n2+2)+...+n/(n2+n)<[n(n+1)/2]/(n2+1)?<1/(n2+1)+ 2/(n2+2)+...+n/(n2+n)<(n2+n)/(2n2+2)而lim (n2+n)/(2n2+2)n→∞=lim (1+ 1/n)/(2+ 2/n2)n→∞=(1+0)/(2+0)=1/2由夾逼準則，得：lim 1/(n2+1)+ 2/(n2+2)+...+n/(n2+n)=1/2n→∞