Step 7 Objective

Identify alternate and corresponding angles; understand a proof that the sum of the angles of a triangle is 180° and of a quadrilateral is 360°.

Examples of what pupils should know and be able to do

Probing questions

How could you convince me that the sum of the angles of a triangle is 180°?

Why are parallel lines important when proving the sum of the angles of a triangle?

How does knowing the sum of the angles of a triangle help you to find the sum of angles of a quadrilateral? Will this work for all quadrilaterals? Why?

What if pupils find this a barrier?

The Year 9 geometrical reasoning mini-pack has many innovative ideas to support pupils' understanding. Use the visualisation exercises to help pupils construct and mentally move images.

Use the build-ups to demonstrate geometrical proof.

Interacting with mathematics in Key Stage 3: Geometrical reasoning mini-pack

Year 10 Bridging Unit Project 4: Developing Geometrical Reasoning