Chapter 10 Lesson 1: Circles and Circumference Objective: Learn to find the circumference of circles.

A circle is the set of all points in a plane that are the same distance from a given point, called the center. The diameter ( d ) is the distance across a circle through its center. The circumference ( C ) is the distance around the circle. The radius ( r ) is the distance from the center to any point on the circle. Pi ( π ) The approximation often used for πis 3.14.

To find the circumference of a circle: To find the circumference of a circle, you have to multiply the diameter ( d ) times Pi ( π ). Or if they just give you the radius, you must multiply 2 times its radius times Pi. There are 2 possible formulas: 1) C= π × d or 2) C = 2 × r × π

Example 1: Find the circumference of the football if it has a diameter of 40 cm. If the formula is C = π × d, then … C = 3.14 × 40 C = cm

Example 2: Find the circumference. The formulas are C = π × d or C= 2 × r × π Since the problem gives you the radius we will follow formula #2. C= 2 × r × π C = 2 × 28m × 3.14 C = m

Your Example: Find the circumference.

Homework: Find the circumference of each circle.