aim: how do we find the circumference and area of a circle? 7g1 7g1 calculate the radius or...

Aim: How do we find the circumference and area of a circle?

7G1 Calculate the radius or diameter, given the circumference or area of a circle.

Do Now:

1.Solve 5 + 2[(92 – 4) + (23 + 1)]

2.Solve and graph x + 11>25

3.Find the LCM of 48 and 90.



diameter d

radius r

circumference C

CIRCLE

Center - the point located in the middle of a circle

Diameter - the distance across the circle through the center.

Radius - the distance from the center to any point on the circle

Circumference: the distance around the circle



Radius r = 3 cm

Diameter d = 6 cm

Diameter is twice the length of the radius.

d = 2r



42 cm

8mm

5 in

Diameter = Radius = Radius =

Find the diameter or radius of each object.

1. 3.2.

10 in 21 cm 4 mm

Find the Diameter or Radius of a Circle



C = dπCircumference of a Circle

C = 2rπ

8mm

C = dπ

= 8π

5 in

C = 2rπ = 2(5)π

= 10π

42 cm

= 42π

C = dπ

Find the Circumference of a Circle

Find the circumference of each object. Round your answer to the nearest tenth.

1. 2. 3.

≈ 25.1mm

≈ 31.4in

≈ 131.9cm



d = 55 cm

1.

2.

r = 18 in

3. r = 2.5 ft


C = dπ C = 2rπCircumference of a Circle

Find the circumference of each object. Round your answer to the nearest tenth. C = dπ

= 55π

≈ 172.8cmC = 2r π = 2(18)

π

≈ 113.1in

= 36π

C = 2r π = 2(2.5) π

≈ 15.7ft

= 5π



5 ft

Practice - Find the circumference of each circle. Round your answer to the nearest tenth.1. 2. 3.

19 in2 mm

1km

100 yd

6. 5. 4.

26 cm




A = πr2

Area of a Circle

8mm 5 in

42 cm

Find the Area of a Circle

Find the area if each object. Round your answer to the nearest hundredth.

A = πr2

A = π42

A = 16π

1. 2. 3.

A = πr2

A = π52

A = 25π

A = πr2

A = π212

A = 441πA ≈ 50.27mm2

A ≈ 78.54in2 A ≈ 1,385.44cm2



Practice - Find the area. Round your answers to the nearest hundredth.

6.3 ft4 mm

1.

10cm

3. 2.

Find the Area of a Circle

A = πr2

A = π52

A = 25π

A ≈ 78.54cm2

A = πr2

A = π22

A = 4π

A ≈ 12.57mm2

A = πr2

A = π6.32

A = 39.69πA ≈ 124.69ft2



Practice - Find the circumference and area. Leave your answer in terms of π.

1. d = 6 cm 3. r = 5 in2. d = 18 mm

Find the Area and Circumference of a Circle

A = πr2

A = π32

A = 9π cm2

C = dπC = 6π cm

A = πr2

A = π92

A = 81π mm2

C = dπC = 18π mm

A = πr2

A = π52

A = 25π in2

C = dπC = 10π in



Find the radius of the circle when given the circumference.

C = 2∏r

1. C = 16 ∏ 2. C = 7 ∏ 3. C = 50 ∏

Find the Radius of the Circle given the Circumference

2∏r= 16 ∏2 2

∏r = 8∏∏ ∏

r = 8

2∏r= 7∏2 2

∏r = 3.5∏∏ ∏

r = 3.5

2∏r= 50∏2 2

∏r = 25 ∏∏ ∏

r = 25



Find the radius of the circle when given the circumference.

C = 2∏r

1. C = 10 ∏ 2. C = 44 ∏ 3. C = 200 ∏


2∏r= 10∏2 2

∏r = 5∏∏ ∏

r = 5

2∏r= 44∏2 2

∏r = 22 ∏∏ ∏

r = 22

2∏r= 200∏2 2

∏r = 100∏∏ ∏

r = 100



Jordan sews a lace border 42π inches long around the edge of a circular tablecloth?

What is the length of the radius from the inside edge of the lace to the center of the circular tablecloth?

42π


2∏r= 42∏2 2

∏r = 21 ∏∏ ∏

r = 21

C = 2∏r

The length of the radius is 21 inches long.

C = 42∏



A circular rug has a circumference of 6π feet. What is the radius of the rug?


2∏r= 6∏2 2

∏r = 3 ∏∏ ∏

r = 3

C = 2∏r

The radius of the rug is 3 feet.

C = 6∏



The circumference of the circle below is 25.12 centimeters. (2006)

What is the best estimate for the length of the radius of the circle?a) 3 centimetersb) 4 centimetersc) 8 centimetersd)16 centimeters

radius

2∏r= 25.122 2

∏r = 12.56

3.14 3.14

r = 4

C = 2∏rC = 25.12

3.14r= 12.56

aim: how do we find the circumference and area of a circle? 7g1 7g1 calculate the radius or...

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