Geometry For Dummies, 3rd Edition
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When you work with circles, there are three straight-line components that you need to be able to identify: radii, chords, and diameters.
  • Radius: A circle’s radius — the distance from its center to a point on the circle — tells you the circle’s size. In addition to being a measure of distance, a radius is also a segment that goes from a circle’s center to a point on the circle.

  • Chord: A segment that connects two points on a circle is called a chord.

  • Diameter: A chord that passes through a circle’s center is a diameter of the circle. A circle’s diameter is twice as long as its radius.

The above figure shows circle O.


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Mark Ryan is the founder and owner of The Math Center in the Chicago area, where he provides tutoring in all math subjects as well as test preparation. Mark is the author of Calculus For Dummies, Calculus Workbook For Dummies, and Geometry Workbook For Dummies.

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