Definition cosd (x:R) : R := cos (toRad x).
Definition tand (x:R) : R := tan (toRad x).

(* Specifications: *)
Lemma Rsqr_sin_cos_d_one : forall x:R, Rsqr (sind x) + Rsqr (cosd x) = 1.
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(**               Other properties                 *)
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Lemma sin_lb_ge_0 : forall a:R, 0 <= a -> a <= PI / 2 -> 0 <= sin_lb a.