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=
由于是等比数列有8a2+a5=0 a5/a2=q^3=-8 所以q=-2
因为Sn=a1(1-q^n)/(1-q)则S5=a1(1-q^5)/(1-q)；S3=a1(1-q^3)/(1-q)
S5/S2=(1-q^5)/(1-q^3)=[1-(-2)^5]/[1-(-2)^3]=-11