Circles – Circumference and Area

Circumference – the distance around a circle

3.14

radius is where2

diameter is where

rrC

ddC

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Example # 1 : The radius of a circle = 4 inches. Find

diameter = ?

circumference = ?

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Example # 1 : The radius of a circle = 4 inches. Find

diameter = 8 inches

circumference = ?

"8

)"4(2

2

d

d

rd

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Example # 1 : The radius of a circle = 4 inches. Find

diameter = 8 inches

circumference = 25.12 inches

"8

)"4(2

2

d

d

rd

"12.25

"814.3

C

C

dC

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Example # 2 : The circumference of a circle = 47.1 feet. Find

diameter = ?

radius = ?

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Example # 2 : The circumference of a circle = 47.1 feet. Find

diameter = 15 feet

radius = ?

d

d

d

feet 1514.3

14.3

14.3

feet 1.47

14.3feet 1.47

Circles – Circumference and Area

Circumference – the distance around a circle

) piletter Greek ( 3.14

radius is where2

diameter is where

rrC

ddC

It turns out, if you divide any circle by its diameter you get pi. Pi is a non-repeating, non-terminating decimal. We’ll always use 3.14 as an approximate value when calculating using Pi.

Example # 2 : The circumference of a circle = 47.1 feet. Find

diameter = 15 feet

radius = 7.5 feet

d

d

d

feet 1514.3

14.3

14.3

feet 1.47

14.3feet 1.47

r

r

r

rd

5.72

2

2

15

215

2

Circles – Circumference and Area

Area of a Circle – the amount of square units inside the circle

2rA

Circles – Circumference and Area

Area of a Circle – the amount of square units inside the circle

2rA

Example 1: The radius of a circle is 3 inches. What is the area?

                                                    

Solution:                    

      = 3.14 · (3 in) · (3 in)      = 3.14 · (9 in2)      = 28.26 in2

2rA

Circles – Circumference and Area

Area of a Circle – the amount of square units inside the circle

2rA

Example 2 : The area of a circle is 78.5 square meters. What is its radius ?

Solution :

r

r

r

r

rA

5

25

14.3

14.3

14.3

5.78

14.35.78

2

2

2

2

Circles – Circumference and Area

Knowing the circumference of a circle can help us find lengths of arcs in circles and central angle measurements.

The total number of degrees in a circle = 360 degrees. We can use proportions to solve these problems.

measure arc

nceCircumfere

measure angle

360

Circles – Circumference and Area

Knowing the circumference of a circle can help us find lengths of arcs in circles and central angle measurements.

The total number of degrees in a circle = 360 degrees. We can use proportions to solve these problems.

Example : Find arc AC if radius = 4 cm and measure of angle AOC = 30 degrees.

C

A

O

2

30°

measure arc

nceCircumfere

measure angle

360

Circles – Circumference and Area

Knowing the circumference of a circle can help us find lengths of arcs in circles and central angle measurements.

The total number of degrees in a circle = 360 degrees. We can use proportions to solve these problems.

Example : Find arc AC if radius = 4 cm and measure of angle AOC = 30 degrees.

C

A

O

2

30°

measure arc

nceCircumfere

measure angle

360

Solution :

cm 12.25

414.32

2

C

C

rC

Circles – Circumference and Area

Knowing the circumference of a circle can help us find lengths of arcs in circles and central angle measurements.

The total number of degrees in a circle = 360 degrees. We can use proportions to solve these problems.

Example : Find arc AC if radius = 4 cm and measure of angle AOC = 30 degrees.

C

A

O

4

30°

measure arc

nceCircumfere

measure angle

360

Solution :

cm 12.25

414.32

2

C

C

rC x

cm 12.25

30

360

cm 09.2

6.753360

x

x

Circles – Circumference and Area

Knowing the circumference of a circle can help us find lengths of arcs in circles and central angle measurements.

The total number of degrees in a circle = 360 degrees. We can use proportions to solve these problems.

Example : Find circumference if arc AC = 24 inches and measure of angle AOC = 60 degrees. .

C

A

O

24

60°

measure arc

nceCircumfere

measure angle

360

Circles – Circumference and Area

Knowing the circumference of a circle can help us find lengths of arcs in circles and central angle measurements.

The total number of degrees in a circle = 360 degrees. We can use proportions to solve these problems.

Example : Find circumference if arc AC = 24 inches and measure of angle AOC = 60 degrees. .

C

A

O

24

60°

measure arc

nceCircumfere

measure angle

360

Solution :

inches 144

60inches 8640inches 2460

360

C

C

C