S3=9/2
a3/q²+a3/q+a3=9/2
a3=3/2代入,整理,得
2q²-q-1=0
(q-1)(2q+1)=0
q=1或q=-½
q=1时,a1=a3=3/2
q=-½时,a1=a3/q²=(3/2)/(-½)²=6
匿名回答于2024-05-14 22:31:22