Question

How do you evaluate `cos (arccos 1.5)`?

Answer 1

`arccos1.5` means: find the angle of which `1.5` is the cosine.

Explanation:

The sine and cosine functions are limited to a range of `{-1,1}`, there is no `arccos1.5` possible.

If the value had been between +1 and -1 then you could have canceled the `arccos` against the `cos` as they are opposite operation (like a root and a square).