(a) Show that a function $f: R \to R$ defined by $f(x) = \frac{2x}{1+x^2}$ is neither one-one nor onto. Further, find set A so that the given function $f: R \to A$ becomes an onto function. OR (b) A relation R is defined on $N \times N$ (where $N$ is the set of natural numbers) as : $(a, b) R (c, d) \iff a-c = b-d$ Show that R is an equivalence relation.