The Six Trigonometric Functions, Basic Introduction, Trigonometry

The unit circle has a radius of one. When a triangle is drawn within it, the hypotenuse is always equal to the radius, which is 1. The coordinates of a point on the circle are represented by x and y, and the angle inside is theta.

For a unit circle (where the radius r=1), sine of theta is equal to the y-coordinate, and cosine of theta is equal to the x-coordinate. An example is given for theta being 30 degrees, where sine 30 is 1/2 and cosine 30 is root(3)/2.

Beyond sine and cosine, there are four other trigonometric functions. Tangent of theta is defined as sine divided by cosine, or y divided by x. Cosecant of theta is 1 over y, secant of theta is 1 over x, and cotangent of theta is x over y. These are the six fundamental trigonometric functions.