Question

Answer 1

\(R2_X=R-R1=20-15=5\Omega\)

\(R2\backslash\backslash\R_X \Rightarrow\dfrac{1}{Rx}=\dfrac{1}{R2x}-\dfrac{1}{R2}=\dfrac{1}{5}-\dfrac{1}{12}=\dfrac{7}{60}\Rightarrow Rx=\dfrac{60}{7}\Omega\)

Answer 2

\(R_1nt\left(R_2//R_x\right)\)

\(\Rightarrow R_1+R_{2x}=R_{AB}=20\Omega\)

\(\Rightarrow R_{2x}=20-15=5\Omega\)

Mà \(\dfrac{1}{R_{2x}}=\dfrac{1}{R_2}+\dfrac{1}{R_x}=\dfrac{1}{12}+\dfrac{1}{R_x}=\dfrac{1}{5}\)

\(\Rightarrow R_x=\dfrac{60}{7}\approx8,57\Omega\)