A circle with a 12 inch diameter has a 6 inch radius.
12 inch
6 inch
6 inches
12 inch diameter(also 6 inch radius).
The radius (not raduis) is 6 inches.
If you are talking about 9 and 12 inch diameter, then divide both by 2 to get the radius. The area of a circle is pi (3.1415 is good for most calculations) multiplied by the square of the radius. So for the 12 inch circle, the radius is 6. The square of the radius is 36, and multiplying this by pi gives approximately 113.1 square inches. Now the 9 inch circle has a radius of 9/2 or 4.5. Squaring this we get 20.25, which multiplied by pi is approximately 63.6 square inches. If 9 and 12 were already the radius in the problem, just don't divide by 2 since you already have the radius.
12 inch diameter(also 6 inch radius).
I assume 12 is diameter. If so 12/2 is radius of 6in. 6x6xpi is 113.1squared inches
The radius of a circle with a 14.5 inch circumference is 2.15 inches
Circumference of a circle = 2*pi*radius or pi*diameter
A 12-inch circle has an area of 0.784 square feet.