What is the equivalent resistor seen from two terminals on the left?

[scanferr]

Homework Statement

R1 = 1K Ohm
R2= 50K Ohm
gM = 100mA/V

I should find the equivalent resistor seen from the two terminals on the left

Homework Equations

Nodes equations, Ohm's law.

The Attempt at a Solution

So, I started by putting a test voltage source on the left but I end up with 2 variables on the equivalent resistor equation that I can't be able to solve.
I did Circuit analysis last year, which I passed but now I'm a bit rusty with this. Anyone can help me?

 

[gneill]

Can you show what you've tried? Show your equations.