Trigonometric ratios Trigonometric ratios are the ratios between edges of a right triangle. These ratios are given by the following trigonometric functions of the known angle A , where a , b and h refer to the lengths of the sides in the accompanying figure: Sine function (sin), defined as the ratio of the side opposite the angle to the hypotenuse . {\displaystyle \sin A={\frac {\textrm {opposite}}{\textrm {hypotenuse}}}={\frac {a}{h}}.} Cosine function (cos), defined as the ratio of the adjacent leg (the side of the triangle joining the angle to the right angle) to the hypotenuse. {\displaystyle \cos A={\frac {\textrm {adjacent}}{\textrm {hypotenuse}}}={\frac {b}{h}}.} Tangent function (tan), defined as the ratio of the opposite leg to the adjacent leg. {\displaystyle \tan A={\frac {\textrm {opposite}}{\textrm {adjacent}}}={\frac {a}{b}}={\frac {a/h}{b/h}}={\frac {\sin A}{\cos A}}....