a1*q^2=a3=3/2
a1(1-q^3)/(1-q)=S3=9/2
q^2(1-q)/(1-q^3)=1/3
3q^2(1-q)=(1-q^3)
2q^3-3q^2+1=0
2q^2(q-1)-(q-1)(q+1)=0,而q≠1
2q^2-q-1=0
(2q+1)(q-1)=0,而q≠1
2q+1=0,q=-1/2
a1=a3/q^2=6
故a1=6 ,q=-1/2

记得采纳啥意思