a2=a1q
a4=a1q^3
a6=a1q^5
a8=a1q^7
a3=a1q^2
a5=q1q^4
a7=a1q^6
(a2+a4+a6+a8)/(a1+a3+a5+a7)=a1q(1+q^2+q^4+q^6)/a1(1+q^2+q^4+q^6)=q=2