The trigonometric functions are also known as circular functions.
The two fundamental trigonometric functions are defined as the coordinates of a any point A travelling around on the unit circle of radius 1 .
The input variable in trigonometric functions is the central angle of the circle 'x' such that we get sin x and cos x which give the x and y coordinates of A.
Hence, the input to a trigonometric function is a central angle of a circle.
