Cosine is a trigonometric function that provides information about the dimensions of an angle using a ratio. An angle can be illustrated geometrically as a slice of a circle. Consider angle AOB positioned within a unit circle centered at the origin (0,0) of the Cartesian coordinate system. A unit circle is defined by x²+y²=1, where 1 is the radius. The vertex of the angle (i.e., the point at which the legs intersect) is at the origin. The initial leg of the angle lies upon the positive x-axis and intersects the circle at point A with coordinates (1,0). The terminal leg intersects the circle at point B, which has the coordinates (x,y).

By definition, the cosine of angle AOB is cos AOB=x/r. This is true for any circle described by x²+y²=r². Because r=1 in this particular case, cos AOB=x (which is the distance from...