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Triangle Angle Sum & Exterior Angle Theorems
- Triangle Angle Theorems
- Exterior Angle Theorem
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Triangle Angle Sum & Exterior Angle Theorems
Jill Casey, Jun 28, 2017
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1. Triangle Angle Theorems
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2. Exterior Angle Theorem
Triangle Angle Theorems
Interact with the applet below for a few minutes.
Then, answer the questions that follow.
Be sure to change the locations of the triangle's WHITE VERTICES each time before you drag the slider!!!
Triangle Angle Sum Theorem
From your observations, what is the sum of the measures of the interior angles of any triangle?
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This is the Triangle Angle Sum Theorem: The sum of the interior angles of a triangle is equal to 180 degrees.
Sum of the Exterior angles of a triangle
From your observations, what is the sum of the measures of the exterior angles of any triangle?
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This is the Sum of the Exterior Angles of a Triangle: The sum of the exterior angles of a triangle is 360 degrees.
Exterior Angle Theorem
Exterior Angle Theorem
Exterior Angle Theorem
The two colored angles are said to be the "remote interior" angles from the labeled exterior angle. What do you think the definition of remote interior angle is?
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The remote interior angles are the angles that are inside the triangle and are not adjacent to the labeled exterior angle.
Exterior Angle Theorem #2
When you moved the slider, the two remote interior angles moved. What did you notice that happened? What do you think the Exterior Angle Theorem is?
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The two remote interior angles added up to the exterior angle. This is the theorem!
Exterior Angle Theorem: An exterior angle of a triangle is equal to the sum of its two remote interior angles
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