Skip to main content
### Number and algebra

### Geometry and measure

### Probability and statistics

### Working mathematically

### For younger learners

### Advanced mathematics

# Impossible Triangles?

NOTES AND BACKGROUND

This problem is all about either finding solutions or proving that there is no solution for any size of triangle shape.

For small triangle shapes, it is easy to check all possible configurations of pieces to check whether a solution exists. For larger triangle shapes the number of combinations of pieces gets larger extremely rapidly, and quickly reaches the point at which a check of all of the combinations is impossible, even on a supercomputer. Even if we have checked a large number of jigsaw sizes and found no solution, this does not necessarily mean that we cannot find a solution for a larger triangle shape. To find a solution, you often need to mine the depths of your cunning and ingenuity. To show that a solution does not exists you often have to use the concept of proof by contradiction .

Proving that a solution**does not** exist is often much easier than proving that a solution does exist. Interestingly, if a solution can be found, then it is usually very quick to check that the solution is correct, although finding the solution in the first place might be exceptionally difficult.This behaviour underlies the notion of the mysteriously titled
'P vs NP' problem, the solution of which will earn the solver $1,000,000

Ideas concerning proof are discussed in the fascinating article Proof: A Brief Historical Survey
## You may also like

### Fixing It

### OK! Now Prove It

Links to the University of Cambridge website
Links to the NRICH website Home page

Nurturing young mathematicians: teacher webinars

30 April (Primary), 1 May (Secondary)

30 April (Primary), 1 May (Secondary)

Or search by topic

Age 16 to 18

Challenge Level

You are given a limitless supply of triangular jigsaw pieces of type T1, T2, T3, T4 and T5

Using these pieces, you need to try to make larger triangular shapes without any overlap.

Three triangle shapes are shown in the picture below. Is it possible to create two-coloured triangles of these shapes without moving the pieces already placed?

Suppose next that you can move the pieces and choose two triangle types to work with. Which pairs of shapes can be used to make larger equilateral triangles? Which pairs of shapes can be used to make larger 30-60-90 triangles? See the video clip for a discussion on this part of the problem

NOTES AND BACKGROUND

This problem is all about either finding solutions or proving that there is no solution for any size of triangle shape.

For small triangle shapes, it is easy to check all possible configurations of pieces to check whether a solution exists. For larger triangle shapes the number of combinations of pieces gets larger extremely rapidly, and quickly reaches the point at which a check of all of the combinations is impossible, even on a supercomputer. Even if we have checked a large number of jigsaw sizes and found no solution, this does not necessarily mean that we cannot find a solution for a larger triangle shape. To find a solution, you often need to mine the depths of your cunning and ingenuity. To show that a solution does not exists you often have to use the concept of proof by contradiction .

Proving that a solution

Ideas concerning proof are discussed in the fascinating article Proof: A Brief Historical Survey

A and B are two fixed points on a circle and RS is a variable diamater. What is the locus of the intersection P of AR and BS?

Make a conjecture about the sum of the squares of the odd positive integers. Can you prove it?