RL circuit: How to determine the equivalent resistance of the circuit?
If you are trying to find the R-L time constant (L/R numerically) then the constant current generator has infinite impedance and can be ignored. This leaves R1 and R3 in series (R1+R3) in parallel with R2 hence the effective resistance of the circuit is: -

R2 || (R1 + R3)

Or do it using Thevenin's theorum; a current source in parallel with a resistor (R1) is equivalent to a voltage source in series with that resistor and this of course makes R1 in series with R3.