This video is about how to ‘rationalise the denominator’ – which is just a way of changing the bottom of a fraction to a whole number – and gives a few examples:

5 divided by 3√2 becomes 5√2 / 6

and

18 divided by √3 becomes 6√3

Like many of these exercises, in isolation, they appear to be fairly irrelevant – it’s only when you need to manipulate equations in higher levels, that they can be useful. Most ‘rationalise the denominator’ questions appear on non calculator GCSE maths papers (including Edexcel, AQA, OCR and Educas), and are approximately grade 6+. The questions are usually 2 – 4 marks.

Please do try some of the questions in the additional posts listed below – with a little practice learning how to rationalise the denominator can be fairly straightforward.

This series of 3 minute math is designed as a quick reminder for some of the main topics. I hope they help to provide a focus and a way forward. If you need any more detail please search the site or contact me – always pleased to answer any questions!

Here’s some additional posts, that might be of interest:

Julius Lucky says

Julius Lucky says

THANK YOU so much Mr Simon. Took me less than 3 minutes to understand what

my teacher took me 30minutes to teach me!

The Universe Of Hannah says

Thank you this was really helpful, but what do i do when it’s: 6+ root 8

root 2 ?

Gyan Chappory says

how can u solve.. 3 root 7 + 3 root 7??

Iuliana Costache says

If only all of the teachers would explain maths the way you do, sir! 🙂

Thank you for posting all of those helpful videos.

Simon Deacon says

Please like and leave a comment!

Visit https://www.3minutemaths.co.uk for real maths, tips and techniques.

Simon Deacon says

Will do – I’ll let you know when posted.

Alex Goody says

Would it be possible to do a video on Set Theory (Venn Diagrams), if so

that would be very useful!

Simon Deacon says

Thanks and glad it helped 🙂

Alex Goody says

Very helpful, keep up the good work !!

Simon Deacon says

Hi – try ‘3 Minute Math – Angles and Number of Sides in Regular Polygons 2’

or ‘3 Minute Math – Angles and Number of Sides in Regular Polygons.’ I hope

these help and all best S

Simon Deacon says

Hi Will – you need to multiply top and bottom by root6. That will give you

3 root6 on the top and 6 on the bottom. If you then divide top and bottom

by 3 you get root6 / 2 Hope this helps and all best S

Will Jolliffe says

Hi ive been asked to rationalise the denominator of 3/root6… the answer

according to the mark scheme is root6/2. Could you tell me how to get to

that answer? Thanks

Simon Deacon says

Will do and will let you know when posted. All the exterior angles of a

regular polygon add up to 360 degrees… the interiors can be calculated by

180 – exterior. Hope this helps and thanks for the request. All best S

Forheloveoflucie21 says

Please can you do a video on finding interior and extirior angles in

regular and irregular polygons?

Simon Deacon says