#### Answer

(b) not defined.
(c) not defined.

#### Work Step by Step

(b) $\cos^{-1}2$ is not defined because $2$ is not in its domain, which is $[-1, 1]$
(c) $\csc^{-1}(1/2)$ is not defined because $\frac{1}{2}$ is not in its domain, which is $ |x|\geq1$.
(a) and (d) are defined because the given values are in the domain of the functions.