高一数学数列请详细解答,谢谢!(3 20:49:46)设Sn是等差数列{an}的前n项和,若S3/S6=1/3,则S6/S1_数学解答

高一数学数列请详细解答,谢谢!(3 20:49:46)
设Sn是等差数列{an}的前n项和,若S3/S6=1/3,则S6/S12=( )
A.3/10 B.1/3 C.1/8 D.1/9

人气：328 ℃　时间：2020-06-26 07:41:51

解答

s3=3a1+3d s6=6a1+15d
S3/S6=3a1+3d /6a1+15d=1/3 化简得a1=2d
S6/S12=6a1+15d/2 /12a1+66d a1=3d代入,所以S6/S12=3/10