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Copy an Angle Construction

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About This MicroSim

This interactive tutorial demonstrates the classical compass and straightedge construction for copying an angle. Adjust the slider to try different starting angles.

Construction Steps

Step Action
1 Draw ray DE (one side of new angle)
2 Draw arc from B intersecting both rays at P and Q
3 Draw arc from D with same radius
4 Measure distance PQ with compass
5 Draw arc from E' with radius = PQ to find F
6 Draw ray DF - the angle is copied!

How to Use

  1. Adjust the slider to change the original angle (20° to 140°)
  2. Click "Next" to advance through steps
  3. Click "Auto" to watch the animation
  4. Click "Reset" to start over

Why It Works

The construction uses arcs to preserve distances: - The first arc ensures equal distances from the vertices - The second arc preserves the "opening" of the angle (distance PQ) - Together, they guarantee the new angle has the same measure

Learning Objectives

  • Perform angle copying construction
  • Analyze how arcs determine angle congruence
  • Apply compass techniques for precision

Bloom's Taxonomy Level

Applying and Analyzing - Performing construction and understanding the method.

Iframe Embed Code

<iframe src="https://dmccreary.github.io/geometry-course/sims/copy-angle/main.html"
        height="652px"
        width="100%"
        scrolling="no"></iframe>