LESSON 7.6AREA AND CIRCUMFERENCE OF CIRCLES

OBJECTIVE:To use formulas for the circumference and area of circles

DEFINITIONSis the set of all points that

is a given distance from a given point.

The given point is the of the circle.

CENTER

A CIRCLE

The given distance is the of the circle, which is a segment with one endpoint on the circle and the other at the center of the circle.

RADIUS

is a segment, with both endpoints on the circle, that passes through the center of the segment.

THE DIAMETER

One diameter equals two radii or d = 2r FORMULAS:

Area of a circle

Circumference of a circle

A = π r2

C = 2πr or C = πd

Find the circumference and the area.

Leave π in the answer. 15 in

C = πd

C = 15π in.

A = πr2

A = π(7.5)2

A = 56.25π in2

Example #1

10 m

C = 2πr A = πr2

C = 2(3.14)(10)

C = 62.8m

A = (3.14)(10)2

A = 314m2

Use 3.14 for π

Example #2

Find the circumference and the area.

Example #3If the circumference of a circle is 8π in., then find the area.

First, we must find the radius.

Then we will use the radius to find the area.

4 in = r

8 π = 2πr

8 π = 2πr 2π 2π

A = πr2

A = π(4)2

A = 16π in2

C = 2πr

Find the radius. Find the area.

Example #44. If the area of a circle is 113.04 m2, then find the circumference. Use 3.14 for π.

First, we must find the radius.

Then we will use the radius to find C

A = πr2

113.04 = (3.14)r2

36 = r2

6 m = r

C = 2πr

C = 2(3.14)(6)

C = 37.68m

Find the radius. Find Circumference

ASSIGNMENT:

7.6 Worksheet Show necessary work

Minimum 3 lines