数列{an}是公差不为0的等差数列,且a1,a3,a7是等比数列{bn}的连续三项,则

问题描述:

数列{an}是公差不为0的等差数列,且a1,a3,a7是等比数列{bn}的连续三项,则
则{bn}的公比q为?

设公差为d
a3=a1+2d,a7=a1+7d
a3/a1=a7/a3
(a1+2d)/a1=(a1+6d)/(a1+2d)
展开消相得a1=2d
q=a3/a1=(a1+2d)/a1=(2d+2d)/2d=2