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=
8a2=-a5
则a5/a2=q³=-8
q=-2
S2=a1*(1-q²)/(1-q)
S5=a1(1-q^5)/(1-q)
所以 S5/S2=(1-q^5)/(1-q²)
=(1+32)/(1-4)
=-11

8a2+a5=0等价于8a2+a2*q^3=0
可得q=-2
s5/s2=(1-q^5)/(1-q^2)=-11