Lesson 10-7 Pages 533-538

Circumference and Area: Circles

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

2. How to find area of circles.

CircleCircle

DiameterDiameter

CenterCenter

CircumferenceCircumference

RadiusRadius (pi)(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 3.1415926... The Greek letter (pi) stands for this number. Using this ratio, you can derive a formula for the circumference of a circle.

d

c dc

What you really need to know!

dc

rc 2

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 = r2

Radius

r

½ of the circumference

½ of 2r

rrA 22

1 2rA

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

35.01408748 = d

At least 35 inches!

Example 4:

Find the area of the circle to the nearest tenth.

A = r2

A = x 112

A = 380.1 ft2

Example 4:

Find the area of the circle to the nearest tenth.

A = r2

A = x 4.152

A = 54.1 cm2

Page 535-536

Guided Practice

#’s 4-9

Pages 533-535 with someone at home and

study examples!

Read:

Homework: Pages 536-538

#’s 10-30 even

#’s 37, 38, 48-53

Practice Quiz 2 #’s 1-5Lesson Check 10-7

Page

749

Lesson 10-7