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# 9.6 Circles

## on Mar 13, 2009

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Chapter 9, Section 6: Circles

Chapter 9, Section 6: Circles

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## 9.6 CirclesPresentation Transcript

• Chapter 9 Section 6: Circles March 11, 2009
• Find Circumference
• A Circle is the set of all points that are the same distance from a given point.
• The given point is the CENTER of the circle.
• Circumference : the distance around the circle.
Center
• 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
• Pi or π
• Pi or π, pronounced “pie,” is the ratio of Circumference (or C) to Diameter (or d).
• C = πd
• C/d = π
• 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.
• Pi
• C = πd
• If the d, or diameter, equals 1, then what is the Circumference (or C)?
• C = π(1), C = π
• Find the circumference of the circle with a diameter of 6ft.
• C = πd  the formula
• C (approx.) = 3.14(6ft)  Substitute
• C = 18.84  Simplify!
6 Feet
• Find the Circumference of Each Circle
• Diameter = 200 miles
• Diameter = 2.8 inches.
• 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.
• Use proportions to find the measures of the central angles.
• Juan’s 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 °
• AT HOME
• Use a cup opening or cap to make your circles if you don’t have a compass.
• 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 °
• 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 °
• 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.