a3*a9=2(a5)^2
a1*q^2*a1*q^8=2(a1*q^4)^2
解得：q=根号下2
a2=a1q=1
a1=根号下2/2a1*q^2*a1*q^8=2(a1*q^4)^2关键是这步不会算不会解出来 ..a1*q^2*a1*q^8=a1^2q^10

2(a1*q^4)^2=2a1^2q^8

∴约掉a1^2q^8得q^2=2
q=根号2我还是看不懂.... a1*q^2*a1*q^8=a1^2q^10乱...

2(a1*q^4)^2=2a1^2q^8