R₁=ρl₁/S₁
R₂=ρl₂/S₂
l₁=2l₂
S₁=πr₁²
S₂=πr₂²
r₁=2r₂=>S₁=4πr₂²=>R₁=ρ*2l₂/4πr₂²=ρl₂/2πr₂²
R₁/R₂=ρl₂/2πr₂²/ρl₂/πr₂²=1/2