{an}等差数列,an=21-2n,bn=|an|,求{bn}的前n项和Tnxx

{an}等差数列,an=21-2n,bn=|an|,求{bn}的前n项和Tnxx 等差数列{an},{bn}的前n项和分别为An,Bn,切An/Bn=2n/3n+1,求lim(n→∞)an/bn 等差数列{an} {bn}前n项和为An Bn,An/Bn=(7n+2)/(4n+27),求an/bn 等差数列{an} {bn}前n项和为An Bn,An/Bn=(7n+2)/(4n+27),求an/bn 计算等差数列{an}{bn}的前n项和分别为An.Bn,且An/Bn=2n/(n+1)求limn→∞(an/bn) 已知等差数列{an},a2=9,a5=21,令bn=n*2^(an),求{bn}的前n项和Sn 十万火急!令bn=n*2^(an)求{bn}的前n项和Sn. 等差数列求和已知{an}=1+(n-1)/2求｛bn｝=1/(n×an) 等差数列除以等比数列 an=n bn=2^n-3 求an除以bn的前n项和 已知等差数列{an},an=21-2n,由知bn=|an|,求数列{bn}的前30项和 已知等差数列an,an=21-2n,又知bn=|an|,求数列{bn}的前30项和 已知数列{an}是等差数列,且bn=an+a(n-1),求证bn也是等差数列 设{an}是等差数列,an=2n-1,{bn}是等比数列,bn=2^(n-1)求｛an/bn｝前n项和Sn 等差数列{An},{bn}的前n项和为An,Bn,且An/Bn=n/3n-2,则a5/b5=? 等差数列{an},{bn}中的前n项和分别是An,Bn,且An/Bn=n/3n-2,则a5/b5=多少 {an}{bn}都是等差数列,已知An/Bn（各自前n项和）=(5n+3)/(2n-1)则an/bn=? 已知等差数列{an}和{bn},他们的前n项之和为An和Bn,若An/Bn=(5n+3)/(2n-1)A9/B9 已知{an},{bn}均为等差数列,前n项的和为An,Bn,且An/Bn=2n/(3n+1),求a10/b10的值 若两个等差数列｛an｝、{bn}的前n项和An、Bn,且满足An/Bn=(4n+2)/(5n-5),则a13/b13