Consider a point situated on a circle with radius A. The circle has a center that coincides with the origin in the cartesian plane. Instead og using the rectangular coordinates to label this point, the x– and y- coordinates at a point on the unit circle given by an angle x (in radians) are defined by the functions x=cosx and y=sinx.
The sine function represents the shift on the y axis of the point by the function of its angle x in radians. The sinus function is defined by the equation f(x) = A sin(x).
The cosine function represents the shift on the x axis of the point by the function of its angle x. The cosine function is defined by the equation f(x) = A cos(x).
These two functions present some common characteristics: