等差数列 2到填空题
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/07/09 05:41:23
等差数列 2到填空题
![](http://img.wesiedu.com/upload/f/b4/fb4068394add874150838729506b51c5.jpg)
![](http://img.wesiedu.com/upload/f/b4/fb4068394add874150838729506b51c5.jpg)
![等差数列 2到填空题](/uploads/image/z/17590460-68-0.jpg?t=%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97+2%E5%88%B0%E5%A1%AB%E7%A9%BA%E9%A2%98+%26nbsp%3B)
{an}与{bn}是等差数列
∴Sn=[n(a1+an)]/2
Tn=[n(b1+bn)]/2
∴Sn/Tn=(a1+an)/(b1+bn)
∵等差数列{an}与{bn}的前n项和的比为2n:(3n+1)
∴(a1+an)/(b1+bn)=2n:(3n+1)
假设(n+1)/2 =k {(n+1)/2为项数}
则n=2k-1
则ak/bk = 2(2k-1)/[3(2k-1)+1]
=(2k-1)/(3k-1)
即an/bn =(2n-1)/(3n-1)
sn=a1+a2+...an=1og2(2/3)+1og2(3/4)+.log2(n+1/n+2)=log2(2/3x3/4x.n+1/n+2)=log2(2/n+2)
∴Sn=[n(a1+an)]/2
Tn=[n(b1+bn)]/2
∴Sn/Tn=(a1+an)/(b1+bn)
∵等差数列{an}与{bn}的前n项和的比为2n:(3n+1)
∴(a1+an)/(b1+bn)=2n:(3n+1)
假设(n+1)/2 =k {(n+1)/2为项数}
则n=2k-1
则ak/bk = 2(2k-1)/[3(2k-1)+1]
=(2k-1)/(3k-1)
即an/bn =(2n-1)/(3n-1)
sn=a1+a2+...an=1og2(2/3)+1og2(3/4)+.log2(n+1/n+2)=log2(2/3x3/4x.n+1/n+2)=log2(2/n+2)