5.已知等比数列{an}\{a_{n}\}{an}的前nnn项和为SnS_{n}Sn,且数列{ka3k−1}(k=1\{ka_{3k-1}\}(k=1{ka3k−1}(k=1,2,3)3)3)是等差数列,则S6S3=(\frac{S_6}{S_3}=(S3S6=( )))