若两个等差数列{an}和{bn}的前n项和分别是Sn,Tn,已知Sn/Tn=7n/(n+3),则a5/b5=

若两个等差数列{an}和{bn}的前n项和分别是Sn,Tn,已知Sn/Tn=7n/(n+3),则a5/b5=
若两个等差数列{an}和{bn}的前n项和分别是Sn,Tn,已知Sn/Tn=7n/(n+3),则a5/b5=

若两个等差数列{an}和{bn}的前n项和分别是Sn,Tn,已知Sn/Tn=7n/(n+3),则a5/b5=
S9/T9
=(a1+a2+...+a9)/(b1+b2+...+b9)
=[(a1+a9)+(a2+a8)+...+(a4+a6)+a5]/[(b1+b9)+(b2+b8)+...+(b4+b6)+b5]
=9a5/(9b5)
=a5/b5
a5/b5=S9/T9=7×9/(9+3)=21/4