Question

How do you evaluate `arccos (0)`?

Answer 1

`arccos0` means: find the angle that has a cosine of `0`

Explanation:

The `cos`-function crosses the `0` every `180 ^o orpi rad`, beginning at `90 ^o or pi/2 rad`

So `arccos(0)=90^o +-k*180^o`

Or `arccos(0)=pi/2+-k*pi rad`

Usually, you are asked to evaluate a function between certain limits, like `0^o <=x<=360^o` or `0<-x<=2pi`
From the above you can find the values that fit.