Geometry For Dummies, 3rd Edition
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The basic idea behind copying a given angle is to use your compass to sort of measure how wide the angle is open; then you create another angle with the same amount of opening.

geometry-angle-compass

Here's the proof diagram.

geometry-copying-angle
Copying an angle.

Refer to the figure as you work through these steps:

  1. Draw a working line, l, with point B on it.
  2. Open your compass to any radius r, and construct arc (A, r) intersecting the two sides of angle A at points S and T.
  3. Construct arc (B, r) intersecting line l at some point V.
  4. Construct arc (S, ST).
  5. Construct arc (V, ST) intersecting arc (B, r) at point W.
  6. Draw line BW and you're done.

About This Article

This article is from the book:

About the book author:

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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