I am currently a sophomore in college, and as of now, my calculus-based physics class is studying the phenomena of mu tual induction. However, the actual text does not display a proof showing that the proportionallity constant of two coils are equal (Msub(2 1) = Msub(1 2) = M, which is then used in the equation EMF = -M(dIsub(1)/dt) and EMF = -M(dIsub(2)/dt) where I is the steady current in the coil(s)), and the professor did not care to address it, saying it should be assumed. Does anyone know this how to go about doing the proof for proving that the proportionallity constant is equal for both coils? I have math background up to and including calculus III and differential equations. Any input would be appreciated. Thanks a lot.