proposition: Lemma cos_mulr2n x : cos (x *+ 2) = cos x ^+2 *+ 2 - 1.
proof: Proof. by rewrite mulr2n cosD -!expr2 sin2cos2 opprB addrA mulr2n. Qed.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(mathcomp_extra boolp classical_sets functions) reals ereal nsatz_realtype signed topology normedtype landau sequences derive realfun exp