An informative lesson contains a brief explanation of how the sum of the angles of a triangle is a line. The lesson continues with determining the missing angle in a triangle, or solving for a variable. Using the sum of the angles, the lesson introduces how to find the measure of an exterior angle of a triangle. 

Concepts

triangles, triangle properties, triangle sum theorem

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Additional Tags

math

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Instructional Ideas

• Review solving linear equations
• Have the class determine why the sum of the angles of a triangle equal 180 degrees

Classroom Considerations

• Make sure the class knows how to solve the types of equations needed 
• The lesson is eighth in an 11-part unit on congruence and similarity

Pros

• Includes a video lecture from a teacher
• Provides several problems of different levels

Cons

• The lesson relies on direct instruction as the sole instructional strategy

Common Core

8.G.A.5 MP2 MP6