∠θ = 30°, cos 30° = adjacent side/hypotenuse = √3:2 = √3/2. Cosine (cos) is a trigonometric function that represents the ratio between the length of the adjacent side and the length of the hypotenuse in a right triangle. In this case, in a triangle with a 30° angle, the length of the adjacent side is half of the length of the hypotenuse, resulting in a ratio of 1:√3:2 for the three sides of the triangle. Trigonometric functions are transcendental functions that belong to elementary functions in mathematics. They represent the mapping between sets of angles and sets of ratios. Typically, trigonometric functions are defined in a plane Cartesian coordinate system, with a domain that extends over the entire real number field. They can also be defined in the context of right triangles, although this is not a complete definition. In modern mathematics, they are described as limits of infinite series and as solutions to differential equations, which allows their definition to be extended to the complex number field.
