Two things I always do when teaching surds:
- Pupils list the first twelve square numbers in their books for reference throughout the lesson. They need to readily recognise square numbers in order to simplify surds so the more they practise listing them, the better.
- When manipulating expressions containing surds (eg expanding brackets) I make comparisons to what they already know about algebra. For example √2 and √3 can be thought of in the same way as x and y (ie not ‘like terms’) whereas 2√3 and 5√3 can be thought of in the same way as 2x and 5x (ie we can add them to get 7√3).
The NCETM suggests a couple of nice ‘hooks’ for getting started teaching surds:
- Ask pupils to find a way of drawing a line with a length of exactly √5 units (the hypotenuse of a right angled triangle with sides 2cm and 1cm)
- Ask pupils to divide the length of an A4 piece of paper by its width. Repeat for A3 and A5. What do they notice? (The answer is always √2)
Here’s some great teaching resources (there's hundreds more online). Most of these work equally well at GCSE and A level:
- Is it rational?
- Two interactive tasks from Mathspad
- Pairs activity
- Introducing surds
- True or false activity
- Surds -Applying and problem solving
- Multiplication squares
- Mr Barton’s activity
- Standards Unit N11
- Surds Connect 4
- Surds resources - leannegadsby on TES
- Manipulating Radicals
- And here’s some resources recommended by the TES.
For a lovely set of surds problems, see my Problem Sets page.
Edit 29/12/14: Thanks to @runningtstitch for suggesting an alternative method for simplifying surds: