Lesson 20.1 Justifying Circumference and area of a circle

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Presentation transcript:

Lesson 20.1 Justifying Circumference and area of a circle Please tear out pages 1077-1088

Circumference & Area of a Circle 𝑅𝑎𝑑𝑖𝑢𝑠=𝑟 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟=2𝑟 𝐶𝑖𝑟𝑐𝑢𝑚𝑓𝑒𝑟𝑒𝑛𝑐𝑒=2𝜋𝑟 or 𝜋𝑑 𝐴𝑟𝑒𝑎=𝜋 𝑟 2

Example 1 – Find the circumference and area of each circle with the given radius or diameter. Round to the nearest tenth. Use 3.14 for 𝜋. 𝑎) 𝑟=14 𝑐𝑚 𝑏) 𝑑=24 𝑓𝑡 𝐶=2𝜋𝑟 𝐶=𝜋𝑑 𝐶=2(3.14)(14) 𝐶=(3.14)(24) 𝐶=28(3.14) 𝐶=75.36 𝑓𝑒𝑒𝑡 𝐶=28(3.14) 𝐴=𝜋 (12) 2 𝐶=87.92 𝑐𝑚 𝐴=(3.14)(144) 𝐴=𝜋 𝑟 2 𝐴=452.16 𝑓𝑡 2 𝐴=(3.14) (14) 2 𝐴= 3.14 196 𝐴=615.44 𝑐𝑚 2

Assignment # Pg. 1082 #2-23 all