http://www.ck12.org Chapter 4. Triangles and Congruence
4.1 Triangle Sum Theorem
Here you’ll learn that the sum of the angles in any triangle is the same, due to the Triangle Sum Theorem.
What if you wanted to classify the Bermuda Triangle by its sides and angles? You are probably familiar with the
myth of this triangle; how several ships and planes passed through and mysteriously disappeared.
The measurements of the sides of the triangle are in the image. What type of triangle is this? Using a protractor, find
the measure of each angle in the Bermuda Triangle. What do they add up to? Do you think the three angles in this
image are the same as the three angles in the actual
Watch This
MEDIA
Click image to the left for more content.CK-12 Foundation: Chapter4TriangleSumTheoremA
MEDIA
Click image to the left for more content.James Sousa:Animation of the Sum oftheInterior Anglesof a Triangle
MEDIA
Click image to the left for more content.James Sousa:ProvingtheTriangle Sum Theorem
Guidance
In polygons,interior anglesare the angles inside of a closed figure with straight sides. Thevertexis the point
where the sides of a polygon meet.
Triangles have three interior angles, three vertices and three sides. A triangle is labeled by its vertices with a 4. This
triangle can be labeled 4 ABC, 4 ACB, 4 BCA, 4 BAC, 4 CBAor 4 CAB. Order does not matter. The angles in any
polygon are measured in degrees. Each polygon has a different sum of degrees, depending on the number of angles
in the polygon. How many degrees are in a triangle?