This post might seem of little importance to some but today I was thinking back to my high school days and (vaguely) remember the 4 quadrants of a Cartesian coordinate plane discussed in class. Depending on the positive or negative sign of a Point's X and Y value, that point in the Cartesian coordinate plane will be located in one of these 4 quadrants.

Quadrant 1 = (+,+)
Quadrant 2 = (-,+)
Quadrant 3 = (-,-)
Quadrant 4 = (-,+)

My interest in this post is about the positive or negative sign of what the Cosine, Sine, and Tangent functions return for the same angle...the angle from one Point to another Point. The sign of these 3 Math functions are different also whenever a Point is located in one of the 4 quadrants.

Quadrant 1 = +Sine,+Cosine,+Tangent
Quadrant 2 = +Sine,-Cosine,-Tangent
Quadrant 3 = -Sine,-Cosine,+Tangent
Quadrant 4 = -Sine,+Cosine,-Tangent

Personally I don't think the order or name of the quadrants are important, as long as you keep them consistent with the coordinate system. For my usage, I order my quadrants "1,2,3,4" clockwise since ActionScript's radians values go clockwise.

I feel this will become useful sometime in the future for me when dealing with angles of Points and determining their positions relative to each other.
In a future situation I might not be given X and Y information, but may only have angle data instead. Seeing the difference of signs from the Cosign, Sine, Tangent output of the angle value will be helpful clues.

So some things come back to haunt you, if they are the ghosts of my math teachers, I will surely pay attention in class this time .