a) Vẽ sơ đồ
\((R_1 nt R_2) // R_3\)
\({R_{12}} = {R_1} + {R_2} = 6 + 12 = 18\Omega \)
\(\dfrac{1}{R_{tđ}} = \dfrac{1}{R_{12}} + \dfrac{1}{R_3} =\dfrac {1}{18}+ \dfrac{1}{18} \)\(\Rightarrow {R_{t{\rm{đ}}}} = 9\Omega\)
+) \((R_3 nt R_2) // R_1\)
\({R_{23}} = {R_2} + {R_3} = 12 + 18 = 30\Omega \)
\(\dfrac{1}{R_{tđ}} = \dfrac{1}{R_{23}} + \dfrac{1}{R_1} = \dfrac{1}{30} +\dfrac {1}{6} \)\(\Rightarrow {R_{t{\rm{d}}}} = 5\Omega\)
\((R_1 nt R_3) // R_2\)
\({R_{13}} = {R_1} + {R_3} = 6 + 18 = 24\Omega \)
\(\dfrac{1}{R_{tđ}}= \dfrac{1}{R_{13}} + \dfrac{1}{R_2}=\dfrac {1}{24} + \dfrac{1}{12} \)\(\Rightarrow {R_{t{\rm{d}}}} = 8\Omega \)
