GEOM 2 | Lesson 1 | Try This! (Sums of Triangle Interior Angles)


Sums of Triangle Interior Angles

Follow the steps below to see one example to show how the sum of the three interior angles of a triangle is determined.

  1. Find a printed copy of a scalene triangle, or draw one on a sheet of paper. Label each angle as 1, 2, and 3.
  2. Cut the triangle out, and tear or cut each of the three corners (see figure below).
  3. Draw a horizontal line, and arrange the triangle corners so that they sit on this line as shown below.

  • What is the angle measure of a line which is also called a straight angle?

  • If all three angles from the triangle form a line, then what is the sum of the angles in a triangle?


Go to Watch (Triangle Sum Theorem)

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