# Teacher Notes

### Why use this resource?

Once students are clear about the fact that if a prime number $p$ divides the product $ab$ then $p$ divides $a$ or $p$ divides $b$, they can go on to show that every integer has a unique prime factorisation. This resource gives the steps of a proof, but students have to sort them into the right order. This is a good way to practise working with a more sophisticated proof than most students would come up with themselves at this stage, and gives students the chance to get used to a more formal style of language and argument.