Check the injectivity and surjectivity of the following functions: (i) f: N → N given by f(x) = x2 (ii) f: Z → Z given by f(x) = x2 (iii) f: R → R given by f(x) = x2 (iv) f: N → N given by f(x) = x3 (v) f: Z → Z given by f(x) = x3