.已知数列的前n项之和为Sn=n2+3n,求证{an}为等差数列,若Sn=n2+3n+1呢?
.已知数列的前n项之和为Sn=n2+3n,求证{an}为等差数列,若Sn=n2+3n+1呢?
已知数列{An}的前N项和Sn=4n2+3n,求证{An}是等差数列
已知数列{an}的前n项和为Sn,满足Sn=2an+n2-4n(n=1,2,3,…).
已知数列{an}的前n项和为Sn=10n-n2.
已知数列{an}的前n项和为Sn,通项an满足Sn+an=1/2(n2+3n-2),求通项公式an.
已知数列{an}的前n项和为Sn=n^2-3n,求证:数列{an}是等差数列
数列{an}的前n项之和Sn=n2+3n+1,则a1+a3+a5等于______.
已知数列{an}的前n项和的公式为Sn=32n-n2,求数列{|an|}的前n项和Sn′.
设数列{an}前n项和为Sn,数列{Sn}的前n项和为Tn,满足Tn=2Sn-n2,n∈N*.
已知数列{an}的前n项和为Sn,且Sn=2n2+n,n∈N*,数列{bn}满足an=4log2bn+3,n∈N*.
已知数列{an}的前n项和,Sn=n2+2n+1.
数列{an}的前n项和为sn=n2+3n+1,则a1+a2+a3+a4+a5