The angle in the diagram is 90 degrees, while the circumferential angle is 360 degrees, so 1/4 of the circle is blank, and the shaded region is 3/4 of the circle. The area of the circle is pi*r^2=36pi cm^2. While the region is only three quarters of it, so the area is 3/4*36pi=27pi cm^2.
The point within the graph is 90 degrees, whereas the circumferential point is 360 degrees, so 1/4 of the circle is clear, and the shaded locale is 3/4 of the circle. The range of the circle is pi*r^2=36pi cm^2. Whereas the locale is as it were three quarters of it, so the zone is 3/4*36pi=27pi cm^2.
