(a) A student wants to pair up natural numbers in such a way that they satisfy the equation $2x + y = 41$, $x, y \in \text{N}$. Find the domain and range of the relation. Check if the relation thus formed is reflexive, symmetric and transitive. Hence, state whether it is an equivalence relation or not. OR (b) Show that the function $f : \text{N} \to \text{N}$, where $\text{N}$ is a set of natural numbers, given by $f(n) = \begin{cases} n - 1, \text{ if } n \text{ is even} \\ n + 1, \text{ if } n \text{ is odd} \end{cases}$ is a bijection.