Trigonometry

Most of these resources are from MATHisFUN.com's - Intro to Trigonometry and Trigonometry

You need to understand the Unit Circle and it's Quadrants

Graphing Coordinates

Artist's rendering of Unit Circle with Quadrants by http://askaniblue.deviantart.com/.
The Unit Circle as illustrated by University of South Florida.

The Unit Circle and the relationships (ratios) of Cosine, Sine, and Tangent

are used to describe the Triangles formed by lines originating in the center of a circle.

Radius, Diameter, Circumference

Radians and Degrees

Interactive unit circle showing the relationships between coordinates, quadrants, angles, and degrees of a circle.

Right Triangle showing hypotenuse, tangent, adjacent, and opposite.
Normal or standard "bell" distribution curve