(1/4 + 1/3 + 1/3) * V1 = I + 2 * I / 3
11 * V1 = 20 * I (1)
V1 = Uab - 4 * I (2)
解得:
Uab = 64 * I / 11
Rab = Uab / I
= 5.818 Ω
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