In a trigonometric circle, function

*f*of \(\mathbb{R}\) in \(\mathbb{R}\) under which all angles of rotation*x*are made to correspond to the*y-coordinate*of a point P of this circle.In the illustration above, sin(*x*) = *k*, where *k* is the y-intercept of point P.

### Symbol

The symbol for the sine function is “sin” and the image of an angle of rotation *x* of this function is written as “sin(*x*)” which is read as “sine x” or “sine of *x*.”

The argument of the function is a number that represents an angle of rotation (and not a figure).