PHYSICS - How was the formula for the magnetic field reached? :/ help!

[hydey]

Hi,

I am currently working through a past paper to prepare me for my own assignments and exams coming up, and I have been doing great up until this question. I am looking for someone to shed some light on it for me please :-) Any experts out there?!

Please view link 1 first for the figure relevant to the question.


LINK 1: http://img.photobucket.com/albums/v242/DickieHyde/photo43.jpg

QUESTION: Consider a general point on the line joining the two wires and a distance away from the mid-point P.

By summing the magnetic field due to currents of magnitude i flowing in both the wires in the senses you found in (c), show that, on the line joibing the two wires, the magnetic fields strength is given by:

Please view Link 2 for the formula.

LINK 2: http://img.photobucket.com/albums/v242/DickieHyde/photo45.jpg

Hint: you may find the identity (a+b)(a-b_ = a^2 - b^2 useful.

[sweetsh]

astarmathsandphysics can help you with this.. I will send him a message

[astarmathsandphysics]

Would love to help, but buth images are cut off at the right hand side.
Please post complete images.