Fuck I don't remember secondary school math 
How do I calculate ??? if I know X?
@matrix sinus or cosinus or tangent, try each and see if answer makes sense :D
@matrix i think it's tangent or cotangent in this case, or rather arc-tangent/arc-cotangent if you need to find angle
@matrix math is fun 
@hj Arctan is bad actually, because when you calculate it with Taylor polynomial it's extremely inaccurate with x < 1.
Why must this programming homework be math?