hi Deon588

I see you have decided to 'take the plunge!'

When you calculate an inverse sine or cosine your calculator will give one value. But really, these trig inverse functions are multi-valued.

eg invcos 1/2 = 60 degree ... but also could be 300 degrees or 360 + 60= 420 or 360 + 300 = 660 or ..........

In order to avoid multiple answers your question is just asking for the 'principle' angle, ie 60 degrees or pi/3 if you want it in rads.

This should be theta + 2k(pi) = invcos(1/2)

By putting k = 1, 2, 3 ... you get all those multiple values.

If you want the principle argument just stop at pi/3 (60)

Bob