arctangent is like arccosine and arcsine.
It's called arc because of the unit circle but there's another name for it I forget what it's like anti ___ I think.
Anyway say I have a number like:
Arctangent is the same:
say I'm looking at:
It's just the opposite of what tangent does, you stuff an angle into tangent, and you get a ratio. For arctan/arcsin/arcos you stuff the ratio and it spits out the angle for that ratio.