(mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)

ratio of the length of the side opposite the given angle to the length of the hypotenuse of a right-angled triangle

the inverse function of the sine; the angle that has a sine equal to a given number

ratio of the adjacent side to the hypotenuse of a right-angled triangle

the inverse function of the cosine; the angle that has a cosine equal to a given number

ratio of the opposite to the adjacent side of a right-angled triangle