Triangle Sum Theorem

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Examples, solutions, videos, worksheets, games, and activities to help Geometry students learn about the angle sum of a triangle.

What is the Triangle Sum Theorem?
The Triangle Sum Theorem states that the sum of the interior angles of a triangle equal 180°.

The following diagram shows an example of the Triangle Sum Theorem. Scroll down the page for examples and solutions.
Triangle Sum Theorem

Triangle Angle Sum
The sum of the three angles in any triangle sum to 180 degrees. The importance of this fact in Geometry cannot be emphasized enough. The triangle angle sum theorem is used in almost every missing angle problem, in the exterior angle theorem, and in the polygon angle sum formula.
This video, discusses the sum of the interior angles of a triangle always equals 180 degrees. There are 4 example problems from easy, medium, medium-hard, and hard.

Angles of a Triangle - Triangle Sum Theorem with Algebra
Students learn the triangle sum theorem, which states that the sum of the measures of the angles of a triangle is 180 degrees. Students are then asked to solve problems related to the triangle sum theorem using Algebra.

Angle Sum of a Triangle

Geometry Word Problems - Angles of a Triangle
The measures of the angles of a triangle are in the ratio 2:5:8. Find the measure of each angle.

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