Without porper bracketings, I am not sure what your question is, so I will assume that it is like this:
1 / [2x(x - 1)] - 3 / [2x]
= 1 / [2x(x - 1)] - 3(x - 1) / [2x(x - 1)]
= [1 - 3(x - 1)] / [2x(x - 1)]
= [1 - 3x + 3] / [2x^2 - 2x]
= [4 - 3x] / [2x^2 - 2x]