公差为d的等差数列{an},d不等于0,a1=0,bn=2^an,Sn是{bn}的前n项和,Tn=Sn/bn

问题描述:

公差为d的等差数列{an},d不等于0,a1=0,bn=2^an,Sn是{bn}的前n项和,Tn=Sn/bn
(1)求Tn
(2)d>0时 limTn

因为是等差数列所以An=a1+(n-1)d则有:a2=a1+da4=a1+3da8=a1+7d又因为A2、A4、A8成等比数列所以a2/a4=a4/a8(a4)2=a2×a8(a1+3d)2=(a1+d)(a1+7d)(a1)2+2(3a1d)+(3d)2=(a1)2+7a1d+a1d+7d22d2=2a1da1...