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9.6 Circles
 

9.6 Circles

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Chapter 9, Section 6: Circles

Chapter 9, Section 6: Circles

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    9.6 Circles 9.6 Circles Presentation 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
      • Radius = 30 millimeters
      • Diameter = 2.8 inches.
      About 628 Miles About 188.4 mm About 8.8 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.