求证1/n+1+1/n+2+...+1/3n+1>1(n属于正整数)
问题描述：
求证1/n+1+1/n+2+...+1/3n+1>1(n属于正整数)
答
用数学归纳法证明当n=1时 左边=1/2+1/3+1/4=13/12>1,成立假设n=k时成立 即1/(k+1)+1/(k+2)+1/(k+3)...+1/(3k+1)>1当n=k+1时 即要证明 1/(k+2)+1/(k+3)+...+1/(3k+1)+1/(3k+2)+1/(3k+3)+1/(3k+4)>1式子里比n=k的式子...