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.

Concepts

triangles, triangle sum theorem, proofs

Show More Show Less

Additional Tags

math

Show More Show Less

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