依题意有(a3)^2=a1*a7即(a1+2d)^2=a1*(a1+6d)所以(a1)^2+4a1*d+4d^2=(a1)^2+6a1*d即a1*d-2d^2=0因为公差不为0所以a1=2d所以数列｛bn}的公比为q=a3/a1=(a1+2d)/a1=(2d+2d)/(2d)=2 公差不为0是题目给的条件
