Internal Angles
In this activity, pupils use dynamic geometry software to explore the internal angles of irregular polygons.
  • Pupils draw a variety of shapes using the software, displaying the internal angles and the sum of the internal angles.
  • They then explore the effect of moving vertices, allowing individual angles to be changed.
  • Teachers invite pupils to offer observations and conjectures about the sum of the internal angles of different polygons.
  • The effect on the sum of moving from a convex to a concave polygon can also be explored.
Some pupils might want to explore external angles or polygons with many sides.

  • Generate terms of a linear sequence using term to term and position to term rules using ICT
  • Explain how to find calculate and use:
    • The sum of the interior angles of triangles, quadrilaterals, pentagons and hexagons
    • The interior angles of polygons
The dynamic geometry software allows pupils to investigate the problem at their own pace. Pupils can explore a wide range of self-generated examples, setting their own level of challenge in the process. The resources include an example of a pupil-generated file which was created using Geometer’s Sketchpad.

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