Question

关于等差数列的一题已知在等差数列中,S3/S6=1/3,求S6/S12?

Answer 1

设等差数列首项为a,公差为d:

S3=3a+3d

S6=6a+15d

S12=12a+66d

由题意：

S3/S6=1/3

即：(3a+3d)/(6a+15d)=1/3

解得：a=2d

∴S6/S12

=(6a+15d)/(12a+66d)

=27d/90d

=27/90

=3/10