设Sn为等比数列｛an｝的前n项和,8a2+a5=0,则S5/S2=

设Sn为等比数列｛an｝的前n项和,8a2+a5=0,则S5/S2=
设Sn为等比数列｛an｝的前n项和,8a2+a5=0,则S5/S2=

设Sn为等比数列｛an｝的前n项和,8a2+a5=0,则S5/S2=
设公比为q
8a2+a2*q^3=0
解得
q=-2
S5/S2
=a1(1-q^5)/(1-q)÷[a1(1-q^2)/(1-q)]
=(1-q^5)/(1-q^2)
=(1+32)/(1-4)
=-11

∵数列{an}为等比数列，且8a2+a5=0
∴8a2=-a5
8=-q³
q³=-8
q=-2
∵S5/S2
=[a1(1-q^5)/(1-q)] / [a1(1-q²)/(1-q)]
=(1-q^5)/(1-q²)
=33/(-3)
=-11

...我看错题目了 不好意思 ....全接错了...