Given the angle of a right triangle in radians, the cosine function returns the ratio of the triangle’s adjacent side over its hypotenuse. For example, given the angle of radians (equivalent to ) the function returns the ratio .
The definition of the cosine function can be visualized by drawing a circle in the cartesian coordinate plane.
Given the angle formed by this circle, the function returns the ratio of the -coordinate divided by the radius of the circle.
The cosine function can be defined using calculus by a Taylor Series approximation.
Derive Cosine Function (Taylor Series) Example