设Sn为等比数列【an】的前n项和,8a2+a5=0,则s5/s2=
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![设Sn为等比数列【an】的前n项和,8a2+a5=0,则s5/s2=](/uploads/image/z/7859151-63-1.jpg?t=%E8%AE%BESn%E4%B8%BA%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%E3%80%90an%E3%80%91%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%2C8a2%2Ba5%3D0%2C%E5%88%99s5%2Fs2%3D)
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