cosine
noun [ C ] mathematics specialized uk/ˈkəʊ.saɪn/ us/ˈkoʊ.saɪn/ (written abbreviation cos)
余弦
(in a triangle that has one angle of 90°) the ratio of the length of the side next to an angle less than 90°, divided by the length of the hypotenuse (= the side opposite the 90° angle)
Compare: sine tangent (TRIANGLE)