Circles are sets of points in a plane that are all the same distance from a central point called the center. The radius is the distance from the center to any point on the circle, while the diameter runs through the center. The circumference of a circle is the distance around it, which can be calculated using the formula C = 2πr. The area of a circle with radius r is calculated as A = πr^2.

1. Basic Geometry Unit 10.7 – Circles: Circumference and Area

2. Story Time…Again!

3. Circles A circle is the set of all points in a plane that are a same distance from a given point in the plane. The given point is called the center .

4. Circles A distance from the center to any point on the circle is called the radius ( r ). The distance across the circle through its center is its diameter ( d ). r d

5. The circumference of a circle is the distance around the circle. The ratio of the circumference of a circle to its diameter is the irrational number called π ( pi ). We often use 3.14 or as approximations.

6. Formulas Circumference of a Circle : If a circle has a radius of r units, then C = 2 π r . Area of a Circle : If a circle has a radius of r units, then the area A is A = π r 2 square units.

7. Find the area and circumference of each circle. Round to the nearest tenth. 5 ½ in. 15.6 m

8. Questions? Homework 10.7 WKS