A "Prove or Disprove" Problem [regarding arccos]

[panic]

Hey everyone. I'm really bad at this sort of thing. Anyway, here goes:


Prove or disprove:

Cos-¹(-x)= π-Cos-¹(x) when x>0

So far, all I know is given

Cos-¹(x)= θ and cosθ=y
0<θ<π

But, I just don't know how to apply it.

Help?
*Note: π is Pi. [I dunno how to write it here]

Thanks so much.. I appreciate this.

/EDIT: Any ideas or suggestions on how I could start this up?

 

[pka]

Know that \(\displaystyle \cos (x) = \cos ( - x)\).

\(\displaystyle \begin{array}{l}
\theta = \arccos (x)\quad \Rightarrow \quad \cos (\theta ) = x \\
\cos (\pi - \theta ) = - \cos (\theta ) \\
\end{array}\)

 

[panic]

Oh, I didn't see your reply..

Thanks a lot, I get it now. :lol: