Bài làm

Ta có $\frac{{{\text{R}}_{\text{1}}}}{{{\text{R}}_{\text{2}}}}\text{=}\frac{\text{ }\!\!\rho\!\!\text{ }\frac{{{\text{l}}_{\text{1}}}}{\text{S}}}{\text{ }\!\!\rho\!\!\text{ }\frac{{{\text{l}}_{\text{2}}}}{\text{S}}}\text{=}\frac{{{\text{l}}_{\text{1}}}}{{{\text{l}}_{\text{2}}}}\Leftrightarrow \frac{\text{2}}{{{\text{R}}_{\text{2}}}}\text{=}\frac{\text{10}}{\text{30}}\Rightarrow {{\text{R}}_{\text{2}}}\text{=6 }\!\!\Omega\!\!\text{ }$