We look at several problems with unknown angles that are solved by using the principle that the angle sum in a triangle is 180 degrees. While the problems can be solved in one's head, I also write an equation for each, since at this (pre-algebra) level students need to practice writing and solving simple equations.

Then, we have a drawing problem: draw an isosceles triangle with 20-cm legs and 40-degree base angles.

Lastly I show you a simple and elegant proof for the fact that the angle sum in a triangle is 180 degrees (or a straight angle). In the proof we use a line that is parallel to the base of our generic triangle. There will be a pair of vertical angles and some corresponding angles formed... check the video to see it all!

Tagged under: angle sum,triangle,180 degrees,angles triangle,angles,proof,pre-algebra,grade 7,math,geometry

Clip makes it super easy to turn any public video into a formative assessment activity in your classroom.

Add multiple choice quizzes, questions and browse hundreds of approved, video lesson ideas for Clip

Make YouTube one of your teaching aids - Works perfectly with lesson micro-teaching plans

1. Students enter a simple code

2. You play the video

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4. You review and reflect

* Whiteboard required for teacher-paced activities

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Clip

Turn any public video into a live chat with questions and quizzes

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Dr Ayla Göl
@iladylayla

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