在等差数列an,bn中,前n项的和分别为Sn,Tn,且Sn/Tn=（7n+2）/（n+3）,则a7/b7=
人气：416 ℃ 时间：2019-10-10 03:27:16
解答
sn/tn=(7n+2)/(n+3) Sn/Tn=n(7n+2)/n(n+3)Sn/Tn=[n(7n+2)/2]/[n(n+3)]/2Sn=n(a1+an)/2Tn=n(b1+bn)/2a1+an=7n+2b1+bn=n+3a7/b7=2a7/2b7=(a1+a13)/(b1+b13)=(7*13+2)/(13+3)=93/16
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