3/2=a3=q^2*a1
9/2=S3=a1+a2+a3=a1+q*a1+3/2
故3q^2=（9/2-3/2）*q^2=(a1+q*a1+3/2-3/2)*q^2
=a1*q^2+a1*q^2*q
=3/2+(3/2)q
解之得
q=1或(-1/2)
若q=1则a1=a3/(q^2)=a3=3/2
若q=（-1/2）则a1=a3/(q^2)=a3=6