设数列公比为q,则a6/a3=243/9=27=q^3,求得q=3,a1=a3/q^2=9/3^2=1;an=a1*q^(n-1)=1*3^(n-1)=3^(n-1)Sn=a1(1-q^n)/(1-q)=1*(1-3^n)/(1-3)=(3^n-1)/2a9=3^(9-1)=3^8s8=(3^8-1)/2