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You know that triangles have angle sums of 180 degrees, but can you prove it? A brief video in the Socratica Geometry series highlights an informal geometric proof. It shows that the sum of the interior angles of a triangle is 180 degrees by using alternate interior angles.
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Concepts
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Instructional Ideas
- Have learners write up a two-column proof of the theorem, if appropriate
Classroom Considerations
- Pupils must have knowledge of angle relationships with two parallel lines and a transversal
- Scholars should also know that a line has 180 degrees
- This video is hosted on YouTube
Pros
- Animations are simplistic, but they help with understanding
Cons
- Marks on diagrams do not distinguish the angles
- Slow-paced video might lose viewers' attention