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 halfjokingly 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
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.
ReplyDeleteYou could use the same technique with parrallelograms. http://mathandmultimedia.com/2011/07/11/anglesofparallelograms/#more10457