1. The problem statement, all variables and given/known data Let two long parallel wires, a distance d apart, carry equal currents I in the same direction. One wire is a x=0 and the other is a x=d. Determine B along the x axis between the wires as a function of X. Repeat problem if wire at x=0 is 2I and in the opposed direction. 2. Relevant equations Answer key = u/2pi * I [(d-2x)/(x(d-x))] 3. The attempt at a solution I understand the physics, but I am unsure how to arrive at that final answer. I do not understand determining the point along the x axis with those variables. Can someone please help me with the deriving?