Question

已知等差数列{an}的公差d≠0,且a1,a3,a9成等比数列,则=(　　)

(A)(B)(C)(D)

 

Answer 1

C

【解析】等差数列{an}中,a1=a1,a3=a1+2d,a9=a1+8d,因为a1,a3,a9恰好构成某等比数列,所以有=a1a9,即(a1+2d)2=a1(a1+8d),解得d=a1,所以该等差数列的通项为an=nd.则的值为.