**"Geometric proof"**

## Tri Fold

*By toni On 30 July, 2021 · Leave a Comment*

Take any triangle and label it ABC with A as the largest angle. Fold the triangle along PQ, PS and QT where the points P and Q are the midpoints of AB and AC and PS and PT are perpendicular to BC.

What do you notice? Why does this happen? Will it […]

## Investigating circle theorems

*By Barrie Barnard On 27 August, 2020 · Leave a Comment*

Activity 1: Finding the centre of the circle

You will need a cut-out paper circle (about 12cm diameter).

Use a circle that does not show the centre. Fold your circle along a diameter. Mark the ends A and B. Now unfold your circle and then fold again along a different diameter and mark the […]

## Pythagoras Similarly

*By toni On 12 July, 2020 · Leave a Comment*

There are hundreds of proofs of Pythagoras Theorem.

This diagram shows a proof.

Look carefully. Can you see three squares?

Assuming that they are squares, can you prove that four of the triangles are congruent?

Can you now write down a proof of Pythagoras’ Theorem and explain the proof?

The second diagram […]

## Encircling

*By toni On 15 July, 2017 · Leave a Comment*

This shape is an equilateral triangle sitting on top of a square.

What is the radius of the circle that circumscribes the shape?

Click here for a hint if you need one to get started.

Click here for the Notes for Teachers.

Click here for the ENCIRCLING poster.

[…]

## Three By One

*By toni On 1 June, 2016 · 2 Comments*

This rectangle measures three units by one unit.

The diagram shows three angles a, b and c.

How many ways can you prove that a + b = c?

What other interesting properties can you find?

When this activity was originally published on NRICH, two boys from Madras School in St Andrew’s, Scotland sent […]

## Geoprob

*By toni On 29 March, 2016 · Leave a Comment*

The point E is inside the square ABCD and AEB is an equilateral triangle. Find the angles EBC, BEC and ECD and give reasons for your answers.

Click for Teacher-Notes-GEO-PROB.

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