S1=2S2 à bạn?
R1 = \(\rho_{Nhôm}\dfrac{l_1}{S_1}\)
R2 = \(\rho_{Nhôm}\dfrac{l_2}{S_2}\)
\(\dfrac{R_1}{R_2}=\dfrac{\rho_{Nhôm}\dfrac{l_1}{S_1}}{\rho_{Nhôm}\dfrac{l_2}{S_2}}=\dfrac{l_1}{S_1}:\dfrac{l_2}{S_2}=\dfrac{l_1}{S_1}\cdot\dfrac{S_2}{l_2}=\dfrac{1}{4\cdot2}=\dfrac{1}{8}\)