(** ** Relation between arcsin, cosine and tangent *)

(* Specifications: *)
Lemma cos_asin : forall x, -1 <= x <= 1 ->
cos (asin x) = sqrt (1 - x²).
Lemma tan_asin : forall x, -1 <= x <= 1 ->
tan (asin x) = x / sqrt (1 - x²).