已知等比数列{An}的公比为q,前n项的和为Sn,且S3,S9,S6成等差数列.

由已知,可得S3=A1(1-q^3)/(1-q);S9=A1(1-q^9)/(1-q);S6=A1(1-q^6)/(1-q);S3,S9,S6成等差数列,所以S3+S6=2S9,化简,得q^3+q^6=2q^9q^3(2q^3+1)(q^3-1)=0,解得,q^3=0(舍去),或q^3=1,或q^3=-1/2当q^3=1时,An=A1,A4,A7的...