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Published byJonathan Cross Modified over 9 years ago
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Circles, Circumference, and Area Section 10-1
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Circle: Definition: A circle is the locus of points in a plane that are a fixed distance from a point called the center of the circle. A has radius r = AB and diameter d = CD.
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Lesson Quiz: Part I 1. Identify each line or segment that intersects Q. chords VT and WR secant: VT tangent: s diam.: WR radii: QW and QR
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Measure the circumference and diameter of a circle and divide the circumference by diameter CircumferenceDiameterC/D
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Cirmumference C = πd
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Example: A drum kit contains three drums with diameters of 10 in., 12 in., and 14 in. Find the circumference of each drum. 10 in. diameter 12 in. diameter 14 in. diameter C = d C = (10)C = (12)C = (14) C = 31.4 in.C = 37.7 in.C = 44.0 in.
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You can use the circumference of a circle to find its area. Divide the circle and rearrange the pieces to make a shape that resembles a parallelogram. The base of the parallelogram is about half the circumference, or r, and the height is close to the radius r. So A r · r = r 2. The more pieces you divide the circle into, the more accurate the estimate will be.
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Area of a Circle: A = πr 2 Find the area of the circle if its diameter is 10. Find the area of the circle if its circumference is 8π.
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