In quadrant III, cosine is negative
In quadrant III, sine is negative
x^2+y^2 = 1 represents the unit circle. This is a circle centered at the origin with radius 1. The point (x,y) is on the unit circle where x = cos(theta) and y = sin(theta)
If theta is between 180 and 270 degrees, then
x = cos(theta) leads to -1 < x < 0, ie x is some negative number between -1 and 0
y = sin(theta) leads to -1 < y < 0, so y has similar properties to x above.
Because we don't know what value theta is exactly, we can only comment on the fact that each result is positive or negative.
The four quadrants are set up where quadrant 1 is in the upper right corner. Then you move counter-clockwise to sweep through the other quadrants 2 through 4.
