{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

∵{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：Sn/Tn=（7n+2）/（n+3）约掉的是knSn=kn(7n+2)a6=S6-S5=264k-185k=79ka5=S5-S4=185k-120k=65ka5/a6=65/79