標上電阻慣用的標號 (R1,R2..) , 如下圖.
你要求的 Rt, 應是指對 V1 兩端.
R1 + R4 = 2
2 // R2 = 2 // 1 (你可以目視為 2 // (2/2) = (1個2)//(2個2並聯) = 3個2並聯) = 2/3
(2/3) + R5 = (2/3) + 1 = 5/3
(5/3) // R3 = (5/3) // 1 (這裡可以目視為 (5/3) // (5/5) = (3個5並聯)//(5個5並聯) = 8個5並聯) = 5/8
5/8 + 1 = (8+5)/8 = 13/8