# The Triangle Sum Theorem and Exterior Angle Theorem

Author:
ctmathnut
Interact with the diagram to answer the questions below: 1. Drag the slider called "Move angles" to place the three corners of the triangle together. What do the three corners form? 2. Based on your findings and your prior knowledge about angle measures, make a conjecture about the sum of the measures of the angles in a triangle. 3. Check the "Show angle measures" box to see if your conjecture from number 2 is correct. This statement about the sum of the angles in a triangle is called the Triangle Sum Theorem. 4. Now click the "Show Exterior Angle" Button. Use what you just learned and your previous knowledge of linear pairs to complete the table below. Based on your findings from the table, make a conjecture about the measure of an exterior angle of a triangle. How can you find the measure of an exterior angle in a triangle? Then check the "Show angle measures" box to check your answer. This relationship is called the Exterior Angles Theorem.