(** * Exercice 2 *)
(* 8:14 *)

Definition fab (a b x : R) : R := (a + b * ln x) / x.

(* Specifications: *)
Lemma Dfab (a b : R) : forall x, 0 < x -> is_derive (fab a b) x (((b - a) - b * ln x) / x ^ 2).
Lemma Val_a_b (a b : R) : fab a b 1 = 2 -> Derive (fab a b) 1 = 0 -> a = 2 /\ b = 2.