• Aug 26th 2011, 02:00 PM
Fenixx09
I have $cos^{-1}(\frac{-1}{2})$

I assume this is the same as $sec(\frac{-1}{2})$

How do I get the "exact value" in radians?
• Aug 26th 2011, 02:11 PM
skeeter
Quote:

Originally Posted by Fenixx09
I have $cos^{-1}(\frac{-1}{2})$

I assume this is the same as $sec(\frac{-1}{2})$

How do I get the "exact value" in radians?

$f(x) = \cos^{-1}(x)$ is the inverse trig function for cosine, not the reciprocal function.

the function's output is an angle.

$\cos^{-1}\left(-\frac{1}{2}\right) = \arccos\left(-\frac{1}{2}\right) = \frac{2\pi}{3}$