The equivalent resistance as seen between the terminals

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The equivalent resistance as seen between the terminals (a, b) is—

1. 2 Ω
2. 4 Ω
3. 1 Ω
4. Not possible

Correct Option: A

R_ab = 1 + (2 || R_ab)

R_AB = 1 +	2.R_ab
	2 + R_ab

R_AB = 1 +	2 + R_ab + 2 R_ab
	2 + R_ab

2 R_ab + (R_ab) ² = 2 + R_ab + 2 R_ab
(R_ab)² – R_ab – 2 = 0
R² _ab – 2 R_ab + R_ab – 2 = 0
R_ab (R_ab – 2) + 1 (R_ab – 2) = 0
(R_ab + 1) (R_ab – 2) = 0
R_ab = – 1, 2
R_ab = – 1 not possible
so R_ab = 2