The triangles in these sets are similar - can you work out the lengths of the sides which have question marks?

Can you help the children find the two triangles which have the lengths of two sides numerically equal to their areas?

Find all the different shapes that can be made by joining five equilateral triangles edge to edge.

The ancient Egyptians were said to make right-angled triangles using a rope with twelve equal sections divided by knots. What other triangles could you make if you had a rope like this?

Arrange the shapes in a line so that you change either colour or shape in the next piece along. Can you find several ways to start with a blue triangle and end with a red circle?

Investigate the different shaped bracelets you could make from 18 different spherical beads. How do they compare if you use 24 beads?

Here is a selection of different shapes. Can you work out which ones are triangles, and why?

In how many ways can you fit two of these yellow triangles together? Can you predict the number of ways two blue triangles can be fitted together?

What do you think is the same about these two Logic Blocks? What others do you think go with them in the set?

Vincent and Tara are making triangles with the class construction set. They have a pile of strips of different lengths. How many different triangles can they make?

How many different triangles can you make on a circular pegboard that has nine pegs?

Can you find all the different triangles on these peg boards, and find their angles?

If you can post the triangle with either the blue or yellow colour face up, how many ways can it be posted altogether?

How many triangles can you make using sticks that are 3cm, 4cm and 5cm long?

What does the overlap of these two shapes look like? Try picturing it in your head and then use the interactivity to test your prediction.

Use the interactivity to find all the different right-angled triangles you can make by just moving one corner of the starting triangle.

Using different numbers of sticks, how many different triangles are you able to make? Can you make any rules about the numbers of sticks that make the most triangles?

Draw three straight lines to separate these shapes into four groups - each group must contain one of each shape.

Can you dissect an equilateral triangle into 6 smaller ones? What number of smaller equilateral triangles is it NOT possible to dissect a larger equilateral triangle into?

Try continuing these patterns made from triangles. Can you create your own repeating pattern?

Can you make the most extraordinary, the most amazing, the most unusual patterns/designs from these triangles which are made in a special way?

This interactivity allows you to sort logic blocks by dragging their images.

How many different ways can you find to join three equilateral triangles together? Can you convince us that you have found them all?

Can you sketch triangles that fit in the cells in this grid? Which ones are impossible? How do you know?

Can you sort these triangles into three different families and explain how you did it?

How many different triangles can you draw on the dotty grid which each have one dot in the middle?

What do these two triangles have in common? How are they related?

Board Block game for two. Can you stop your partner from being able to make a shape on the board?

Take it in turns to make a triangle on the pegboard. Can you block your opponent?

I cut this square into two different shapes. What can you say about the relationship between them?

Have you noticed that triangles are used in manmade structures? Perhaps there is a good reason for this? 'Test a Triangle' and see how rigid triangles are.

This ladybird is taking a walk round a triangle. Can you see how much he has turned when he gets back to where he started?

Jennifer Piggott and Charlie Gilderdale describe a free interactive circular geoboard environment that can lead learners to pose mathematical questions.

Make a flower design using the same shape made out of different sizes of paper.

Use the interactivity to investigate what kinds of triangles can be drawn on peg boards with different numbers of pegs.

Have a go at making a few of these shapes from paper in different sizes. What patterns can you create?

Can you each work out what shape you have part of on your card? What will the rest of it look like?

This article for teachers suggests activities based on pegboards, from pattern generation to finding all possible triangles, for example.

What is the total area of the four outside triangles which are outlined in red in this arrangement of squares inside each other?

Using a loop of string stretched around three of your fingers, what different triangles can you make? Draw them and sort them into groups.

Cut a square of paper into three pieces as shown. Now,can you use the 3 pieces to make a large triangle, a parallelogram and the square again?

This practical problem challenges you to create shapes and patterns with two different types of triangle. You could even try overlapping them.

Can you work out what shape is made by folding in this way? Why not create some patterns using this shape but in different sizes?

Can you find out how the 6-triangle shape is transformed in these tessellations? Will the tessellations go on for ever? Why or why not?

Liethagoras, Pythagoras' cousin (!), was jealous of Pythagoras and came up with his own theorem. Read this article to find out why other mathematicians laughed at him.