> Alex indicates to get ARCTan They're simply the inverses...   arctan (
tan(x) ) = x
What I don't understand is how to get arctan from a tan fraction
>

You could do that by intelligent iteration.
eg to get arctan(y)
Propose some answer z = arctan(y)
Take tan(z).
Note whether tan(z) is higher or lower than y.
Adjust z and repeat.
Brute force and not (probably) a good use of processing power, but easy if
you only have the tan function available.
It could be "optimised" by making some intelligent assumptions about the
approach to the correct value based on the known shape of the tan curve.

I'm sure Scott D has a far superior answer :-)


        RM

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