The third quadrant is contained in the segment of the circle X1AY1 and is lettered III. It
contains the angles between 180 and 270.
The fourth quadrant is contained in the segment of the circle Y1AX and is lettered IV. It
contains the angles between 270 and 360.
c. If you begin at the line AX and rotate a radius through 360, you can construct any number
of right triangles in each of the four quadrants shown in Figure 4-11. The radius will represent the
hypotenuse of the right triangle, a perpendicular line from the intersection of the radius and the circle to
Figure 4-10. The coordinate system
Figure 4-11. Quadrants of a circle