Sn=a1(q^n-1)/(q-1)=93 1
an=a1q^(n-1)=48 2
1式除2式得
(q^n-1)/(q-1) / q^(n-1)=93/48
(2^n-1)/(2-1) / 2^(n-1)=93/48
(2^n-1)/2^(n-1)=93/48
(2^n-1)/(2^n*1/2)=93/48
(2^n-1)/2^n=93/(48*2)=93/96
96(2^n-1)=96*2^n-96=93*2^n
3*2^n=96
2^n=32=2^5
n=5