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Tool: Exterior Angles of a Triangle - Math Open Reference
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An interactive applet and associated web page that demonstrate the exterior angles of a triangle. The applet shows a triangle where the user can drag any vertex to reshape it. The exterior angles are shown and a running calculation shows that no matter how you change the triangle,

  1. the exterior angles always add up to 360°
  2. An exterior angle is equal to the sum of the opposite interior angles

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at

Technology Type: Java Applet 
Author: John Page
Language: English 
Cost: Does not require payment for use

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Courses: Geometry Exterior, Triangles