Does someone know why it is not possible to obtain the network equivalent resistance as seen from the terminal a-b by short circuiting the voltage sources and doing network reduction in this case? Could it have something to do with the dependent voltage source \(6I_x\)

By Network Reduction:

\( R' = 4 || 6 = 2.4 \Omega \)

Applying KVL on the open circuit a-b

\( -20 + 4I_x - 6I_x + 6I_x = 0 \)

\(

I_x = 5 (A)

V_{oc} = 30 V

\)

Applying KVL on the short circuit a-b

\(

I_x = 0

-20 + 4I = 0

I_{sc} = 5 A

\)

By Thevenin's Theorem:

\( R' = \frac{V_{oc}}{I_{sc}} = 6 \Omega\)