Disproof by Counter Example (Edexcel IAL Maths)

Spec point — 1.3

Disproof by counter example

What is disproof by counter example?

• Disproof by counter examples involves finding a value that does not work for the given statement

  • That value is called a counter example

How do I disprove a result?

• You only need to find one value that does “not work”
• Numbers that have unusual results are often helpful to try

• Look carefully to see what types of number the result is claimed for – it may just be integers rather than real numbers
• Irrational numbers can be unusual
• Think about areas of maths where unusual things happen – such as in trigonometry where there are several angles with the same sine value

Worked Example