Unit Circle

0 degrees, 90 degrees, 180 degrees, and 369 degrees is used for the Unit Circle. Also, 0, pie/2, pie, 3 pie/2, 2pie is used in radians.

In these formulas, the angle tells you the point:

Sin theta= y/r
Cos theta= x/r
Tan theta= y/x
Csc theta= r/y
Sec theta= r/x
Cot theta= x/y

The unit circle's center is located at (0,0) and the radius is 1.

If it's at 0 degrees, 369 degrees, 0, or 2 pie, you use the point (1,0)
90 degrees or pie/2 use (0,1)
180 degrees or pie use (-1,0)
270 degrees or 3pie/2 use (0,-1)

Quadrant 1 is between points (1,0) and (0,1)
Quadrant 2 is between points (0,1) and (-1,0)
Quadrant 3 is between points (-1,0) and (0,-1)
Quadrant 4 is between points (0,-1) and (1,0)

Ex. Find
A. Sin 180 degrees
Sin is y/r and y is 0 and r is always 1
B. Cos 180 degrees
Cos is x/r and x is -1 and r is always 1

Ex. State if the expression is positive, negative, or zero
A. Sin 60 degrees
60 degrees is between 90 and 180 degrees. Sin is y/r the y is positive over r which is 1. So the answer is positive
B. Cos 300 degrees
300 degrees is between 270 and 360 degrees. Cos is x/r the x is positive over r which is 1. So the answer is positive