It's only a ArcTangent function call.
AngYX = 180 * Atn(Y / X) / 3.1415926536
AngZY = 180 * Atn(Z / Y) / 3.1415926536
AngZX = 180 * Atn(Z / X) / 3.1415926536
Also, you can search for BillSoo's ArcTangent function in the code library for negative vector components.
Also, you'll have to convert the Arctangent radians into degree by multiplying by 180 and dividing by Pi.