# Interactive video lesson plan for: Angles in a triangle add up to 180 degrees - exercises and proof

#### Activity overview:

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

Play this activity

1. Students enter a simple code

2. You play the video

3. The students comment

4. You review and reflect

* Whiteboard required for teacher-paced activities

## Ready to see what elsecan do?

With four apps, each designed around existing classroom activities, Spiral gives you the power to do formative assessment with anything you teach.

Quickfire

Carry out a quickfire formative assessment to see what the whole class is thinking

Discuss

Create interactive presentations to spark creativity in class

Team Up

Student teams can create and share collaborative presentations from linked devices

Clip

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

### Spiral Reviews by Teachers and Digital Learning Coaches

@kklaster

Tried out the canvas response option on @SpiralEducation & it's so awesome! Add text or drawings AND annotate an image! #R10tech

Using @SpiralEducation in class for math review. Student approved! Thumbs up! Thanks.

@ordmiss

Absolutely amazing collaboration from year 10 today. 100% engagement and constant smiles from all #lovetsla #spiral

@strykerstennis

Students show better Interpersonal Writing skills than Speaking via @SpiralEducation Great #data #langchat folks!