Trigonometric Functions: Unit Circle Geometry

Visualize all six trigonometric functions as lengths associated with the unit circle. Adjust the angle using the slider.
Explain the names of the tangent and secant functions. What do the three functions with "co-" in their names have in common? By looking at the geometry, how can you tell the sign (+/-) of each function for any given angle? Where (if anywhere) is each function undefined? Explain using the geometry. Identify the three similar triangles. What does this relation tell us about the relationship of the functions?