Imatfaal's maths may well be sound, but he was under the misapprehension that I was ignoring terms which had I² on the denominator.

What I should have said is that I have ignored terms containing m²/I².

Sure.

 

Keep trying. I'm sure you'll figure out how this was done eventually.

Agree with Iggy - keep soldiering on! As is probably obvious from above, I am not a great fan of losing terms too quickly unless and until the calculation becomes too difficult or they are clearly insignificant (ie if they are just cumbersome then leave and in but get a bigger sheet of paper)

You can lead a horse to water

but some things they just can't be forced to swallow