a2a610S5201的精选

问题详情：已知等差数列{an}的前n项和为Sn,且a2+a6=10,S5=20.(1)求an与Sn;(2)设数列{cn}满足cn=,求{cn}的前n项和Tn.【回答】解(1)设等差数列公差为d,S5==5a3=20,故a3=4,a2+a6=2a4=10,故a4=5,∴d=1,an=a3+d(n-3)=n+1,易...