专题升级训练26 解答题专项训练(数列)
1.(2012·云南昆明质检,17)已知等差数列{an}的前n项和为Sn,a2=3,S10=100.
(1)求数列{an}的通项公式;
(2)设bn=nan,求数列{bn}的前n项和Tn.
2.(2012·山东济南二模,18)已知等比数列{an}的前n项和为Sn,且满足Sn=3n+k,
(1)求k的值及数列{an}的通项公式;
(2)若数列{bn}满足=(4+k)anbn,求数列{bn}的前n项和Tn.
3.(2012·河南豫东豫北十校段测,18)已知数列{an}的前n项和为Sn,a1=1,Sn=nan-n(n-1)(n∈N*).
(1)求数列{an}的通项公式;
(2)设bn=,求数列{bn}的前n项和Tn.