Lesson 10-7 Pages Circumference and Area: Circles

What you will learn! 1. How to find the circumference of circles. 2. How to find area of circles.

CircleDiameter Center Circumference Radius  (pi)

What you really need to know! A circle is the set of all points in a plane that are the same distance from a given point.

What you really need to know! The ratio of the circumference of a circle to its diameter is always equal to The Greek letter  (pi) stands for this number. Using this ratio, you can derive a formula for the circumference of a circle.

What you really need to know!

The area A of a circle equals the product of pi (  ) and the square of its radius r. A =  r 2 Radius

r ½ of the circumference ½ of 2  r

Example 1: Find the circumference of the circle to the nearest tenth. C =  d C =  x 12 C = 37.7 in

Example 2: Find the circumference of the circle to the nearest tenth. C =  d C =  x 14.2 C = 44.6 m

Example 3: A landscaper has a tree whose roots form a ball- shaped bulb with a circumference of about 110 inches. How wide will the landscaper have to dig a hole in order to plant the tree?

Example 3: C =  d 110 =  d = d At least 35 inches!

Example 4: Find the area of the circle to the nearest tenth. A =  r 2 A =  x 11 2 A = ft 2

Example 4: Find the area of the circle to the nearest tenth. A =  r 2 A =  x A = 54.1 cm 2

Page Guided Practice #’s 4-9

Pages with someone at home and study examples! Read:

Homework: Pages #’s even #’s 37, 38, Practice Quiz 2 #’s 1-5 Lesson Check 10-7

Page 749 Lesson 10-7