In a
trigonometric circle, function
f of [latex]\mathbb{R}[/latex] in [latex]\mathbb{R}[/latex] 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).
Example
The graphic representation of the base function defined by
f (
x) = sin(
x), x being the measure of the angle in radians, is: