Respuesta :

mathmate
Use
a(i)=a1*r^(i-1)
we know that a(5)=a1*(1/2)^(5-1)=a1/16 = 1/4
solve for a1=(1/4)*16=4
=>
sequence: 
4,2,1,1/2,1/4,1/8,1/16,...