设Sn是公差不为0的等差数列{an}的前n项和,且S1,S2,S4成等比数列,则a2a1等于(  ) A.1 B.2 C.3 D.4

问题描述:

设Sn是公差不为0的等差数列{an}的前n项和,且S1,S2,S4成等比数列,则

a2
a1
等于(  )
A. 1
B. 2
C. 3
D. 4

由S1,S2,S4成等比数列,
∴(2a1+d)2=a1(4a1+6d).
∵d≠0,∴d=2a1

a2
a1
=
a1+d
a1
=
3a1
a1
=3.
故选C