Saturday, August 6, 2011

Demonstrating angle sum of triangle using an IWB

Here is a quick demo of how to show the angle sum of a triangle using an Interactive Whiteboard and SMART Notebook, starting with blank screen. It's surprisingly quick and fun to do - my Year 7 class hooted in delight.

 Grab a triangle from the shapes menu.
 Use three different colour pens to mark the angles - can be as messy as you wish!
 Group the triangle with the three coloured paint patches  to make a single object.
 Clone the group twice to make three identical triangles.
 Grab the second triangle by the rotation handle and start rotating it.
 Drag the second triangle to join the first triangle, aligning so two different coloured angles are adjacent.
 Bring in the third triangle, aligning so the third angle is adjacent to the other two.
 The three angles line up to form a straight line = 180 degrees. QED!

My Year 7 class loved this - they half-jokingly suggested I was rigging it - and insisted I try out different triangles and watched very intently to see if I was sneakily stretching or adjusting the triangles.  Enjoy - but don't miss out doing it the traditional way with a paper triangle and cutting off the angles - nothing beats hands on feel for maths.

Next in this series: IWB Tips: Making invisible algebra visible

1 comment:

1. Love it, so simple, I love it when they don't believe you and start trying different versions. I'd think about using Jing or the page recorder and have the students teach it to the class, record it and embed it in Edmodo for future revision.

You could use the same technique with parrallelograms. http://mathandmultimedia.com/2011/07/11/angles-of-parallelograms/#more-10457