Circumference and Area of Circles

A circle is a shape consisting of all points in a plane that are a fixed distance (radius) from a central point (center).

The formula for the circumference of a circle is $$C = 2\pi r$$ or $$C = \pi d$$ .

The diameter of a circle is twice the length of the radius. $$d = 2r$$ .

The area is $$A = \pi r^2 = \pi (5)^2 = 25\pi \approx 78.5 cm^2$$ .

Circumference refers to the distance around the circle.

To convert diameter to radius, divide the diameter by 2. $$r = \frac{d}{2}$$ .

The area is $$A = \pi r^2 = \pi (6)^2 = 36\pi \approx 113.1 cm^2$$ .

The circumference is $$C = 2\pi r = 2\pi (3) = 6\pi \approx 18.85 m$$ .

The formula for the area of a circle is $$A = \pi r^2$$ .

The diameter is 16 inches, calculated as $$d = 2r = 2(8)$$ .