Equalities that involve trigonometric functions and are true for every single value of the variables that are defined. These functions are useful when a problem with a trig function must be simplified

A function of an angle, or of an abstract quantity, used in trigonometry, including the sine, cosine, tangent, cotangent, secant, and cosecant, and their hyperbolic counterparts.

The unit circle is used to understand sines and cosines of angles found in right triangles. The unit circle has a center at the origin (0,0) and a radius of one unit. Angles are measured starting from the positive x-axis in quadrant I and continue around the unit circle. The ray from the origin to a point on the circle (x,y) will give the trigonometric functions of the angle through the coordinates.