sn是等差数列｛an}前n项和,若s3/s6=1/3,求s6/s12

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sn是等差数列｛an}前n项和,若s3/s6=1/3,求s6/s12
sn是等差数列｛an}前n项和,若s3/s6=1/3,求s6/s12

sn是等差数列｛an}前n项和,若s3/s6=1/3,求s6/s12
设等差数列首项为a,公差为d,可以计算出
S3=3a+3d
S6=6a+15d
S12=12a+66d
S3/S6=1/3
则（3a+3d）/（6a+15d）=1/3
解得a=2d
所以S6/S12=3/10

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