a1a2a4的精选

问题详情：已知等差数列{an}的前n项和为Sn,满足S3=12,且a1,a2,a4成等比数列.(1)求an及Sn;(2)设bn=,数列{bn}的前n项和为Tn,求Tn.【回答】解(1)设等差数列{an}的公差为d,因为S3=12,且a1,a2,a4成等比数列,所以有即解得所...