Take three different colour sheets , place one over the other and draw a triangle on the top sheet. Cut the sheets to get triangles of different colour which are identical. Mark the vertices and the angles as shown. Place the interior angles `angle1,angle2` and `angle3` on a straight line, adjacent to each other, without leaving any gap. What can you say about the total measure of the three angles `angle1,angle2` and `angle3` ?


Can you use the same figure to explain the ''Exterior angle property'' of a triangle ? If a side of a triangle is stretched, the exterior angle so formed is equal to the sum of the two remote interior angles.