S6/S3=(1-q^6)/(1-q^3)=1+q^3=3故q^3=2S9/S6=(1-q^9)/(1-q^6)=7/3
若S6/S3=3所以(A4+A5+A6)=2(A1+A2+A3) A7+A8+A9=2(A4+A5+A6)所以S9/S6=7/3
