# How do you evaluate  cos (arccos 1.5)?

$\arccos 1.5$ means: find the angle of which $1.5$ is the cosine.
The sine and cosine functions are limited to a range of $\left\{- 1 , 1\right\}$, there is no $\arccos 1.5$ 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).