Circle: Circumference and Area

The circumference (C) of a circle is given by the formula: C = $$\text{π} \times d$$ or C = $$2 \times \text{π} \times r$$ , where d is the diameter and r is the radius.

The area (A) of a circle is given by the formula: A = $$\text{π} \times r^2$$ , where r is the radius.

The radius is half the diameter. This can be expressed as: r = $$\frac{d}{2}$$ .

The radius is 5, since r = $$\frac{d}{2}$$ = $$\frac{10}{2}$$ .

The circumference is 18.84, calculated as C = $$2 \times \text{π} \times r = 2 \times 3.14 \times 3$$ .

The diameter is 8, since d = $$2 \times r = 2 \times 4$$ .

The circumference is 15.7, calculated as C = $$\text{π} \times d = 3.14 \times 5$$ .

The area is 12.56, calculated as A = $$\text{π} \times r^2 = 3.14 \times 2^2$$ .

The distance around a circle is called the circumference.

If the radius is doubled, the area increases by a factor of four, since A = $$\text{π} \times (2r)^2 = 4 \times \text{π} \times r^2$$ .