# How do you evaluate sec^-1(-1)?

May 2, 2017

$\pi$

#### Explanation:

You are looking for an angle, $\theta$, whose secant is -1.
Since $\sec x = \frac{1}{\cos} x$, this is the same as looking for an angle whose cosine is -1.

This is one of the standard angles, which one should have memorized. The inverse cosine provides values between 0 and $\pi$ only.

The exact value is $\pi$ radians or 180 degrees.