Step 9 Objective

Explain how to find, calculate and use the interior and exterior angles of regular polygons.

Examples of what pupils should know and be able to do

Probing questions

How can you use the angle sum of a triangle to calculate the sum of the interior angles of any polygon?

If the polygon is regular, what else can you calculate?

What if pupils find this a barrier?

The Year 9 geometrical reasoning mini-pack - Acrobat pdf document (148Kb) includes an interesting approach to proving the sum of the interior angles of a regular polygon. See notes in phase one of the unit plan on page 8 of the booklet.