问题描述: 设等差数列{an}的公差为d不为0,a1=9d,若ak是a1与a2k的等比中项,则k= 1个回答 分类:综合 2014-09-23 问题解答: 我来补答 a1=9d ak=a1+(k-1)*d=9d+(k-1)*d a2k=a1+(2k-1)*d=9d+(2k-1)*d ak^2=a1*a2k 化简后可求出k=4 展开全文阅读