Đáp án:
* Cách 1 :
$\dfrac{1}{R_{tđ}} = \dfrac{1}{R1} + \dfrac{1}{R2}$
$⇒ \dfrac{1}{R_{tđ}} = \dfrac{1}{15} + \dfrac{1}{10}$
$⇒\dfrac{1}{R_{tđ}} = \dfrac{10}{150} + \dfrac{15}{150}$
$⇒\dfrac{1}{R_{tđ}} = \dfrac{1}{6}$
$⇒R_{tđ} = 6$ (Ω)
* Cách 2 :
$R_{tđ} = \dfrac{R1 . R2}{R1 + R2} = \dfrac{15 . 10}{15+10} = \dfrac{150}{25} =6 $ (Ω)