# 9.6 Circles

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Chapter 9, Section 6: CirclesTRANSCRIPT

- 1. Chapter 9 Section 6: Circles March 11, 2009

2. Find Circumference

- ACircleis the set of all points that are the same distance from a given point.

- The given point is theCENTERof the circle.

- Circumference : the distance around the circle.

Center 3. Inside the Circle

- Radius : a line segment that starts on the circle and ends at the center point.

- Chord : segment whose end points are on the circle.

- Diameter : a chord that passes through the center of the circle

4. Pi or

- Pi or , pronounced pie, is the ratio of Circumference (or C) to Diameter (or d).

- C = d

- C/d =

- Pi is constant =3.14159265358979323846

- Pi as a fraction = 22/7

- Because every circle is the same, the ratio is always the same, which is why pi is a constant.

5. Pi

- C =d

- If the d, or diameter, equals 1, then what is the Circumference (or C)?

- C = (1), C =

6. Find the circumference of the circle with a diameter of 6ft.

- C =dthe formula

- C (approx.) = 3.14(6ft)Substitute

- C = 18.84 Simplify!

6 Feet 7. Find the Circumference of Each Circle

- Diameter = 200 miles

- Radius = 30 millimeters

- Diameter = 2.8 inches.

About 628 Miles About 188.4 mm About 8.8 inches 8. Making Circle (Pie) Graphs

- A CENTRAL ANGLE is an angle whose vertex is the center of a circle.

- There are 360 in a circle.

- To make a Pie Graph, find the measure of each central angle by finding the proportion.

9. Use proportions to find the measures of the central angles.

- Juans Weekly Budget :

- Lunch (l) = 25%

- Recreation (r) = 20%

- Clothes (c) = 15%

- Savings (s) = 40%

Find the percentage of 360 to find the degree measurement of the central angles. L = 90 R = 72 C = 54 S = 144 10. AT HOME

- Use a cup opening or cap to make your circles if you dont have a compass.

11. Blood Types of Population

- Tell me the degree measurements of the central angles if you were to make a Pie graph with this information.

43% 5% 12% 40% Type O Type AB Type B Type A 155 18 43 144 12. Students at Western High School: Find Central Angles.

- Students at Western High School work in the following places; restaurants, 140; library, 15; auto shop, 60; retail stores, 75; and other places, 30. Round the measures of the central angles to the nearest degree.

Restaurant: 158 Retail: 84 Auto Shop: 68 Other: 34 Library: 17 13. Assignment #16:

- Pages 472-473: 1-24. Skip #20.

- Remember, if you need a circle and have no compass, then use a cup from home and trace the outside.