138. 如下圖所示電路,a、 b 兩端之戴維寧等效電壓 VTh 及 等效電阻 RTh 為何? 統測 113(A) VTh = 12V、RTh = 6Ω(B) VTh = 18V、RTh = 6Ω(C) VTh = 18V、RTh = 3Ω(D) VTh = 12V、RTh = 3Ω