(2014•齐齐哈尔三模)等差数列{an}的前n项和为Sn,且S3=6,a1=4,则公差d等于( ) A.1 B.53 C.-2 D.3
问题描述:
(2014•齐齐哈尔三模)等差数列{an}的前n项和为Sn,且S3=6,a1=4,则公差d等于( )
A. 1
B.
5 3
C. -2
D. 3
答
∵S3=6=
(a1+a3),且 a3=a1+2d,a1=4,∴d=-2,3 2
故选C.