Experiment: Sum of the Angle Measures in a Triangle

Objective

This experiment is designed to help students learn that the sum of the three interior angle measures of any triangle is always 180°. This is not intended to be a formal proof. Please consult the corresponding content section if additional information is needed.

User´s Guide

This program provides an interactive environment in which students can easily change the triangle to any desired type: acute, obtuse, or right triangle, by simply dragging any of the vertices of the triangle. As the results show, the sum of the angle measures in a triangle is always 180° regardless of the shape of the triangle.

 
 
 
 
Experiment: Sum of the Angle Measures in a Triangle
Suggested Experiments

  1. Try to generate a series of acute triangles (all three angles less than 90°). What is the sum of the angle measures?
  2. Try to manipulate the triangle to form a series of obtuse triangles while watching the numerical display to make sure one angle is larger than 90°. What is the sum of the angle measures?
  3. Try to maintain one of the angles as a right angle while dragging the other two vertices to form new right triangles. What is the sum of the angle measures in each case?