Quick question about finding Thevenin equivalents

[DWill]

Homework Statement

When finding the Thevenin resistance for a circuit, there is a method involving applying either a test voltage source or a test current source at the terminals a and b. My teacher didn't really go into this in very much detail so I was wondering if you can specify any value for the test sources? i.e. I can place an arbitrary voltage source (say 5 V) at the terminals, find the current I_t through the source and have R_Th = 5/I_t?

Thanks

Homework Equations

The Attempt at a Solution

 

[rootX]

Yes.