maths

guys help how do you know which wave function to use

You could probably guess the min/max values and where they occur for this simple one, but as its sin(x)-cos(x), it would probably be simplest to use sin(x-alpha) as that way both sin(alpha) and cos(alpha) are positive so alpha lies in quadrant 1.

You can use others, but you may need to be a bit more careful about calculating alpha...

Oh right, kinda forgot about that

Its one of those things not to worry about too much, though if alpha is in quadrant 2 or 3, you have to be careful if you do a naive atan() calculation.