You are given the R_3 resistance valueiwonder wrote:But wouldn't you need to know the resistance of R3 to use the standard method like what you mention, chalker?

Chalker, I understand what you saying , because you can basically can find R_x with R_3 by only taking 2 voltages and using ohms law twice, but as iwonder said that method defeats the purpose the wheatstone bridge :/ .

One could do that process with R_1 and the Potentiometer, then you could find the potentiometer's resistance, then calculate R_x. At least that way you use the Potentiometer's resistance to find R_x.