Proof by Contradiction (AQA A Level Maths): Revision Note

Proof by Contradiction

What is proof by contradiction?

• A proof by contradiction assumes the opposite result is true

• Then, through a series of logical steps, shows that this cannot be so

How do I do proof by contradiction?

• This type of proof often involves explanation in words alongside mathematical statements

• Start with a statement assuming the opposite is true

  • e.g. 'Assume...'

• Use prime factorisation to write a composite number as a product of primes