等差数列{an},{bn}的前n项分别为Sn,Tn,若Sn/Tn=2n/3n+1,则an/bn=多少?
人气:270 ℃ 时间:2019-08-19 13:40:19
解答
∵{an}与{bn}是等差数列∴Sn=[n(a1+an)]/2Tn=[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...
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