Question

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

Answer 1

`pi`

Explanation:

You are looking for an angle, `theta`, whose secant is -1.
Since `secx = 1/cosx`, 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.