设Sn是等差数列｛an｝的前n项和,若a5/a3=5/9,则S9/S5值为?_其他解答

设Sn是等差数列｛an｝的前n项和,若a5/a3=5/9,则S9/S5值为?

人气：495 ℃　时间：2019-09-22 10:15:38

解答

S9/S5=[(a1+a9)*9/2]/[(a1+a5)*5/2]
=(9/5)*(a1+a9)/(a1+a5)
=(9/5)*(2*a5)/2*a3)
=(9/5)*(5/9)
=1