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, a powerful method of mathematical proof.
This article for pupils and teachers looks at a number that even the great mathematician, Pythagoras, found terrifying.
We are given a regular icosahedron having three red vertices. Show that it has a vertex that has at least two red neighbours.