an=0.5^n*sin(nπ/2),Sn为其前n项和求极限Sn

已知等差数列｛an｝的前n项和为Sn,且a1不等于0,求（n*an)/Sn的极限、（Sn+Sn+1）/(Sn+Sn-1) 等差数列{an}前n项和为Sn=3n-2n^2,求an 数列{An}的通项An=n^2（cos^2(n π)/2-sin2(nπ/3)）,其前n项和为Sn,求S30, 数列{an}的通项an=n²(cos²nπ/3-sin²nπ/3),其前n项和为Sn. 已知数列 an前n项和为Sn,a1=1,Sn=2a(n+1),求Sn 等比数列中,sn为前n项和,sn=2an—1,求an 数列{an}前n项和为Sn,且2Sn+1=3an,求an及Sn 已知数列An中,其前n项和为Sn,A1=1,且An+1=2Sn,求An的通项公式和Sn 已知数列{an}的通项公式an=log2[(n+1)/(n+2)](n∈N),设其前n项的和为Sn,则使Sn 已知数列{an}中,an=n(2的n次方-1),其前n项和为Sn,则Sn+1/2n(n+1)等于? an=（2^n-1）/2^（n-1）前n项和为Sn,求Sn 等差数列｛an｝前n项和为Sn,且Sn=3n^2+n 求公差d