thanks for:

http://www.emesystems.com/BS2math3.htm#arcCos

but in my application, i am not using x or y...

i am just getting a phase shift from a Phase Locked-Loop, transforming this number to degree and then, i need the cosine of this number...

All the problem is that "cosine" was made to give an answer in two's complement... and this is bad...... i need the normal answers...