Angles in a Triangle

Today we looked at angle sums in grade 9. I don’t have a before picture, but I cut out some triangles, labelled their angles A,B,C, then ripped them up to put the angles all together to form a straight line.

We did the same thing for a quadrilateral, labelling the angles, ripping it up and placing the angles together to form a full circle, 360 degrees.

Next we looked at exterior angles, and how they always add up to 360 degrees. You can do this with paper too, but I hadn’t been careful enough when I cut out the shapes earlier. This video also gets the point across, and when played in a loop is quite calming and meditative.

We then started to solve equations to find missing angles. This is our introduction to solving, which is a change to my previous sequence. I think it’s a nice introduction since the values we are finding are all positive, and we can practice writing equations all in context of solving for a missing angle.