Guest Post

This is a post about an activity that I didn’t get to witness, but I heard about in the planning stages, and saw pictures of the fun. The grade 10 class was introducing the equation of a circle.

They started by building right angle triangles with a hypotenuse of 20cm, and a uniquely specified side length. Some worked in red, others pink, others blue, and others purple.

The triangles were all put up into one big picture on the board. One acute angle was on the origin, and one of the legs of the triangle was on the x axis. Blue and purple went into the negatives, and red and pink were positive values.

When placed, together there began to be some patterns emerging.

Not only did they see that each of the quadrants had triangles, they noticed that some were longer, and some were taller. More triangles were made to fill in the gaps, and to see the shape that emerged.

There’s a circle that forms. The coordinates of the point on the circle come from the side lengths (x and y) of the perpendicular sides of the right triangle. The radius is the hypotenuse of the right triangle.

This was a neat way to connect ideas about right triangles and access some of that prior knowledge, and connect it to new learning about circles. By working hands-on everyone was participating and contributing to building the over-all picture.

I’m looking forward to trying this when I teach 2D again.