\(a,\)\(\Rightarrow\left\{{}\begin{matrix}\dfrac{R1}{R2}=\dfrac{l1}{l2}\Rightarrow\dfrac{2}{R2}=\dfrac{5}{10}\Rightarrow R2=4\Omega\\\dfrac{R1}{R3}=\dfrac{l1}{l3}\Rightarrow\dfrac{2}{R3}=\dfrac{5}{15}\Rightarrow R3=6\Omega\end{matrix}\right.\)\(\Rightarrow R\left(dây\right)=R1+R2+R3=12\Omega\)
\(b,R1//R2//R3\Rightarrow\dfrac{1}{Rtd}=\dfrac{1}{.R1}+\dfrac{1}{R2}+\dfrac{1}{R3}\Rightarrow Rtd=1,09\Omega\)
\(c,\) \(cần\) \(ghép\) \(R1nt\left(R2//R3\right)\)\(\Rightarrow Rtd=R1+\dfrac{R2R3}{R2+R3}=4,4\Omega\)
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