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问题: 数列027

等差数列{an}和{bn}中前n项和分别为Sn,Tn,若Sn/Tn=2n/(3n+1),则Lim(an/bn)(n趋近于无穷大)等于多少?

解答:

∵ An/Bn=2An/2Bn=[A1+(2n-1))]/[B1+B(2n-1)]=S(2n-1)/T(2n-1)=2(2n-1)/[3(2n-1)+1]=(2n-1)/(3n-1),
∴ Lim(an/bn)(n→∞)=Lim(2n-1)/(3n-1)=2/3