Trigonometric Baby Steps

I've taken my first steps at learning trigonometry this week. I've been working on a game that uses pseudo-trajectory and mathematical collision detection. I thought it a good chance for me to dunk my head into the quicksand that is trig.

My most used function? Math.atan2. I can't recommend it enough for finding angles. The basics of it goes like this:

ObjectA has an X and a Y coordinate and ObjectB also has an X and a Y coordinate. Start with one object (I'll start with ObjectA) and subtract each axis from each other.

var nRun:Number = ObjectA._x - ObjectB._x;
var nRise:Number = ObjectA._y - ObjectB._y;

Math.atan2 takes these two numbers as arguments like so:

var nRadians:Number = Math.atan2(nRise,nRun);

There you have it. You now know, in radians, what angle ObjectA points at ObjectB. If you want to see it in degrees so you can rotate your movie clip:

var nDegrees:Number = nRadians / Math.PI * 180;