S3=A1+A2+A3=3A1+3d
S6=A1+A2+.+A6=6A1+15d
(3A1+3d)/(6A1+15d) = 1/3
3(A1+d)=(2A1+5d
A1=2d
A2=3d A3=4d
S6/S12=(2d+3d+4d+5d+6d+7d)/(2d+3d+.+13d) =27/88
设Sn是等差数列｛an｝的前N项和,诺S3/S6=1/3则S6/S12=多少
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