Question

{an},{bn}是两个等差数列,其前n项和分别为Sn和Tn,且Sn/Tn=（7n+2）/（n+3）,求a5/a6

Answer 1

∵{an},{bn}是两个等差数列

Sn/Tn=（7n+2）/（n+3）

∴[n/2(a1+an)]/[n/2(b1+bn)]=(7n+2)/(n+3)

∴(a1+an)/(b1+bn)=(7n+2)/(n+3)

∴a5/b5=(2a5)/(2b5)=(a1+a9)/(b1+b9)

=(7×9+2)/(9+3)=65/12

求a5/a6缺条件：