Circumference Bell Ringers

Transcription

1 Circumference Bell Ringers 1. A pair of jeans cost to make. If Old Navy marks up the jeans by 45%, what will be the cost of the jeans. 2. Bobby makes a 8% commission on a house that sold for 250,000. How much will he make in commission. 3. A computer is on sale for after a 20% discount. What is the original price of the computer. 4. I go out to lunch and buy a sandwich for 6.99, drink for 1.25, and a cookie for.99. If sales tax is 9% and I leave a 20% tip what will my total bill be?

2 7.G.4 Circumference of a Circle

3 Circles A circle is the set of all points in a plane that are the same distance from a given point, called the center.

4 The diameter (d) is the distance across a circle through the center of the circle. Circles The circumference (C) is the distance around a circle. The area (A) is the amount of twodimensional space taken up by an object. The radius (r) is the distance from the center to any point on the circle.

5 Circles Pi is a non-terminating and non-repeating number represented by the Greek letter (pi) 3.14 is often used as an approximation for.

6 To Find Area of a Circle The Area (A) of a Circle is found by using the following formula: Squared or to the second power: radius x radius A = Area Radius: The distance from the center to the edge of a circle It is half of the circle's diameter.

7 Circles - Area Formula for finding the area of a circle: A = r 2 If you are given the diameter instead of the radius; divide the diameter by 2 to get the radius.

8 Calculate the area of the following circle Area = π r 2 First, you must find half of your diameter: 2 2 = 1 A = π 1 2 A = π 1 x 1 A = 3.14 x 1 A = 3.14 yd 2

9 Calculate the area of the following circle Area = π r 2 A = π 5 2 A = π 5 x 5 A = 3.14 x 25 A = 78.5 km 2

10 Calculate the area of the following circle What is the area of a circle with a diameter of 5 meters? Area = π r 2 First, you must find half of your diameter: 5 2 = 2.5 A = π A = π 2.5 x 2.5 A = 3.14 x 6.25 A = m 2

11 Calculate the area of the following circle A clock s minute hand is 7.0 inches long. How much area it sweeps in 1 hour? Area = π r 2 A = π A = π 7 x 7 A = 3.14 x 49 A = in 2

12 Calculate the area of the following circle A circular linen tablecloth has a diameter of 70 inches. How many square inches of linen was required to make this tablecloth? Area = π r 2 First find the radius by dividing the diameter in half: 70 2 =35 A = π 35 2 A = π 35 x 35 A = 3.14 x 1225 A = in 2

13 Calculate the area of the following circle A sheep is tied to a post in the field. If the length of the rope is 45 feet, what is the area of the field in which the sheep can graze? Area = π r 2 A = π 45 2 A = π 45 x 45 A = 3.14 x 2025 A = ft 2

14 Finding a Circle s Circumference Formulas for finding Circumference C = d C = 2 r If you are given the diameter in a problem use the formula with d. If you are given a problem with the radius use the formula with r. Both formulas find the circumference.

15 Find Circumference C = 2 r C = 2 (21) C = 2 x 3.14 x 21 C = inches 21 in

16 Your Turn Find the Circumference C = d C = (4.5) C = 3.14 x cm C = 14.13cm

17 How are Circumference and Area Related How can we find circumference given the area. A= in 2 Think of the formulas: A= π r 2 C = 2 π r What do both formulas have in common? The radius = π r = 3.14 r = 3.14r = r 2 (To find the opposite of squared you need to find the square root. ) 36 = r2 r = 6 C= 2 π r C = 2 π 6 C = 2 x 3.14 x 6 = in

18 Calculate the circumference of the following circle. A = ft 2

19 Calculate the circumference of the following circle. A = yd 2

20 How are Circumference and Area Related C = in

21 Calculate the area of the following circle. C = yd

22 Calculate the area of the following circle. C = 62.8 yd