proposition: Lemma cosN x : cos (- x) = cos x.
proof: Proof. have /eqP := sinN_cosN x. rewrite paddr_eq0 => [/andP[_]||]; try exact: sqr_ge0. by rewrite sqrf_eq0 subr_eq0 => /eqP. 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