设an是等差数列bn是等比数列,记anbn的前n项和分别是Sn,Tn,若a3=b3,a4=b4,s5-s3/T4-T2=5,则a5+a3/b5+b3=

Question

设an是等差数列bn是等比数列,记anbn的前n项和分别是Sn,Tn,若a3=b3,a4=b4,
s5-s3/T4-T2=5,则a5+a3/b5+b3=

Answer 1

a3=b3,a4=b4
q=b4/b3=a4/a3
q=(a1十3d)/(a1十2d)
(s5-s3)/(t4-t2)=5
5a1十10d-3a1-3d=10a1十25d
4a1十9d=0
a1=-9d/4
q=-3
a5十a3/b5十b3
=2a4/a3十9a3
=a4/6a3
=(-9d/4十3d)/(-27d/2十12d)
=3d/4÷(-3d/2)
=-1/2