串联时,U/I = R1+R2
并联时,16I/3U = 1/R1 + 1/R2 = (R1+R2)/R1R2
可得,R1R2 = 3U^2/16I^2
可解得R1=3U/4I,R2=U/4I
R1:R2=3:1