已知Sn,Tn分别是等差数列{an}与{bn}的前n项和,且Sn/Tn=2n+1/4n-2(n=1,2..,则a10/(b3+b18)+a11/(b6+b15)=麻烦今天马上解决,谢谢拉

Question

已知Sn,Tn分别是等差数列{an}与{bn}的前n项和,且Sn/Tn=2n+1/4n-2(n=1,2..,则a10/(b3+b18)+a11/(b6+b15)=
麻烦今天马上解决,谢谢拉

Answer 1

因为｛an｝、｛bn｝是等差数列,
因此 a10+a11=a1+a20 ,b3+b18=b6+b15=b1+b20 ,
所以,a10/(b3+b18)+a11/(b6+b15)
=a10/(b1+b20)+a11/(b1+b20)
=(a10+a11)/(b1+b20)
=(a1+a20)/(b1+b20)
=[(a1+a20)*20/2]/[(b1+b20)*20/2]
=S20/T20
=(2*20+1)/(4*20-2)
=41/78 .