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
等于( )a2 a1
A. 1
B. 2
C. 3
D. 4
答
由S1,S2,S4成等比数列,
∴(2a1+d)2=a1(4a1+6d).
∵d≠0,∴d=2a1.
∴
=a2 a1
=
a1+d a1
=3.3a1
a1
故选C