Joining two wires, magnetic fields and a little algebra

[shyguy79]

Homework Statement

Consider a general point on the line joining the two wires and a distance d
away from the mid-point O. By summing the magnetic field due to currents of magnitude i flowing in both the wires which are non-zero, show that on the line joining the two wires, the magnetic field strength is given by:

B= μ iD / π(D2 −d2)

Homework Equations

(D^2 −d^2) = (D+d)(D-d) ****** a simple trig identity
B= μ i / 2π d

The Attempt at a Solution

I'm kinda stuck - any pointers on where to start?

 

[shyguy79]

Just bumping it back up - anyone any ideas?