a1a2a12
=a1*a1q*a1q^11
=a1³*q^12=64
(a1q^4)³=64
a1q^4=4
a3a5
=a4²
=a1²*q^6=8
a1q^4=4
所以a1²q^8=16
所以q²=2
q>0
q=√2
a1=4/q^4=1
所以an=(√2)^(n-1)
a1a2a12
=a1*a1q*a1q^11
=a1³*q^12=64
(a1q^4)³=64
a1q^4=4
a3a5
=a4²
=a1²*q^6=8
a1q^4=4
所以a1²q^8=16
所以q²=2
q>0
q=√2
a1=4/q^4=1
所以an=(√2)^(n-1)