getting distance from angles

....or triangulation.

I would like to use two angles on a triangle and the distance between them to calculate the distance to the third angle. there are a few ways to do this, although I can't remember them at the moment but what is the BEST way to do it in C++? I need accuracy to +-.05 or better more than I need speed but both is better. It will not always be an Isosceles. the only constant will be the distance between the two angles.

I started learning C++ on my own about a week ago but I can write a program to calculate most of the more simple mathematical formulas.