已知等比数列{an}的前n项和为Sn,且a3=2,S3=3/2,求a6.问步骤中
问步骤中
s3=a1(1-q^3)/(1-q)=a1(1+q+q^2)=3/2,
a1(1-q^3)/(1-q)怎么得到a1(1+q+q^2)?