已知等比数列{an}的前n项和为Sn,a3=2,a6=16,求S6/S3的值
问题描述:
已知等比数列{an}的前n项和为Sn,a3=2,a6=16,求S6/S3的值
答
a3=a1*q^2,a6=a1*q^5,
a6/a3=q^3=16/2=8
S6/S3
=a1*(q^6-1)/(q-1)÷a1*(q^3-1)/(q-1)
=(q^6-1)/(q^3-1)
=q^3+1
=8+1
=9