Trigonometry maths help

[Amleto]

Sorry, but this isn't right.

To give an extreme example, what direction to you need to go from (90, 80) to (-90, 80)? The arctan(long_difference/lat_difference) implies you should go due East, but you should actually go due North.

i dont know anything about lat/long - which way round are the coords? looks like the answer is 0 to me => north