If all resistances in the provided image are equal ...find I/I'.....and pls explain how to go forward with such questions

 Here by symmetry the lower vertex of the triangle which is she is a note that means the current coming to that junction will go up straight into another side of the triangle not to the line which is present with that voltage source this is nodal method and thus you can see a wheatstone bridge then it becomes easy you get I in lower and upper branch then I Dash becomes Tu I