Resources tagged with: Proof by contradiction

There are 3 NRICH Mathematical resources connected to Proof by contradiction, you may find related items under Thinking Mathematically.

Broad Topics > Thinking Mathematically > Proof by contradiction

An Introduction to Proof by Contradiction

Age 14 to 18

An introduction to proof by contradiction, a powerful method of mathematical proof.

The Dangerous Ratio

Age 11 to 14

This article for pupils and teachers looks at a number that even the great mathematician, Pythagoras, found terrifying.


Age 14 to 16
Challenge Level

We are given a regular icosahedron having three red vertices. Show that it has a vertex that has at least two red neighbours.