Circumference and Area of Circles

The formula for the circumference of a circle is $$C = \frac{\text{d}}{2} \times \text{π}$$ or $$C = 2\text{π}r$$ , where d is the diameter and r is the radius.

The formula for the area of a circle is $$A = \text{π}r^2$$ , where r is the radius.

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

The diameter is $$d = 2r = 2 \times 7 = 14 \text{ cm}$$ .

The circumference is $$C = \text{π}d = \text{π} \times 10 \text{ cm} \ \text{(approximately } 31.42 \text{ cm)}$$ .

The circumference is $$C = 2\text{π}r = 2 \times \text{π} \times 5 \text{ cm} \ \text{(approximately } 31.42 \text{ cm)}$$ .

The area is $$A = \text{π}r^2 = \text{π} \times 3^2 = 9\text{π} \text{ cm}^2 \ \text{(approximately } 28.27 \text{ cm}^2)$$ .

The value of π (pi) is approximately 3.14.

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

The circumference is $$C = \text{π}d = \text{π} \times 8 \text{ cm} \ \text{(approximately } 25.13 \text{ cm)}$$ .