proposition: Lemma cos_coeff_2_4 : cos_coeff 2 4%N = 2%:R / 3%:R :> R.
proof: Proof. rewrite /cos_coeff /= mul1r -exprnP sqrrN expr1n mul1r 2!factS mulnCA mulnC. by rewrite 3!exprS expr1 2!mulrA natrM -mulf_div -2!natrM divff// mul1r. 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