Let R[x] denote the set of all polynomials in x with real coefficients. On R[x], define a
relation ~ by f(x) ~g(x) if f'(x) = g'(x), where f'(x) is the derivative of f(x). Show that ~ is an equivalence relation on R[x]. For any f(x) E R[x], determine the equivalence class [f(x)].