Instructional Video

Parallel Lines and Triangles

Curated and Reviewed by Lesson Planet

Triangles bring sums to geometry. The lesson presents two theorems dealing with the angles of a triangle. Pupils learn about the Triangle Sum Theorem and the Exterior Angle Theorem, and then apply the theorems to create equations and find missing angles.

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CCSS: Adaptable
Instructional Ideas
  • As a class, develop the proof of the Exterior Angle Theorem
Classroom Considerations
  • Requires knowledge of solving equations
  • Fourth section of a seven-part Parallel and Perpendicular Lines unit
  • This video is hosted on YouTube
Pros
  • Demonstrates the two-column proof of the Triangle Sum Theorem
  • Answer key shows the solving steps in finding the solution to the problem
Cons
  • None