Category Archives: Core

349. Circumcircle Investigation

The A-level textbook we use has a nice picture of the circumcircle of a triangle and a definition, plus a brief description of how to work through them. For those who are pondering what a circumcircle is, click on the image or link below

Image credit: WolframMathWorld

I’ll just stick to basic vocabulary in this post, rather than the formal circumcentre and circumradius.

Back to the book – not exactly inspiring or memorable stuff!

I looked at the class and off the cuff changed the lesson plan.


  • Plain paper
  • Pencil
  • Ruler
  • Compasses
  • Calculator

Step 1

Draw a decent size triangle on the paper. Label the corners A,B,C.

Step 2

Using geometrical constructions, find the centre of the circle that your triangle fits in. Check by actually drawing the circle

Step 3

Discuss what techniques gave the best results – hopefully you’ll have perpendicular bisectors. There is a nice comparison between bisecting the angles (which some students will do) and bisecting the sides. The angle bisectors always cross inside the triangle, the side bisectors don’t.

Step 4

Randomly generate co-ordinates for A, B, & C. Get the students to pick them and then they can’t moan if the calculations are awful.

Step 5

Discuss how you are going to find the centre and radius of the circumcircle. We decided on:

  • Only use two sides
  • Find the midpoints
  • Find the gradients and hence perpendicular gradients
  • Generate the equations of the lines through the midpoint
  • Find where they intersect
  • Use the point and one corner to find the radius

Step 6

Review their methods, looking for premature rounding in questions. I’m still instilling an appreciation for the accuracy of fractions and surds, over reaching for the calculator.

Step 7

This is how my solution looked – I numbered the picture and the steps so students could follow the logic. I was answering on one page projected on screen.


313. Friendly Functions

Just a quick resource share today!

I’ve been doing functions with my GCSE class as part of the new curriculum and I’ve gone down the algebra route. I could have started with graph drawing like the parallel class did, but I know my class – drawing and accuracy are not their forte. We made brilliant progress with substituting into functions and even composite functions went smoothly. I wasn’t happy with the textbook resources on manipulating functions so I put together a step by step resource, including a basic skills recap:

Manipulating functions (docx)

Manipulating functions (pdf)

I also thought my class needed a little hand holding for inverse functions. There are many ways to do this, but the method I used was designed to allow the class to access the topic with teacher input verbally and on the board.

Inverse Functions worksheet (docx)

Inverse Functions worksheet (pdf)

Hope these help!

Oh and you can even use them as A-Level recap tools.

Updated (19:53): To fix typo on Inverse functions worksheets

312. Class Commentary

I don’t know about you, but going over higher level questions (eg A-Level) after a test can be a frustrating time. The students never seem to fully engage because they think they know it all – even though they do get things wrong! What if I could offer you a way to review the test and incorporate an understanding of exam board mark schemes?

Image credit:


  • When you mark the test clearly indicate on the paper which questions students got fully correct.
  • Alternatively get your students to do this.

Set Up

  • List the question numbers on the board
  • Starting with the highest number (usually the hardest questions) students volunteer to answer the questions on the board by putting their name next to a question number. In this way the brightest students who got the tricky questions right can’t volunteer to do the easier questions, allowing other students a chance of success.
  • Long multi-part questions could have more than one student.
  • You can also allocate a calculation checker and algebra checker if you have spare students


  • Bring up each student to go through a question on the board.
  • Whilst they do this you can do a commentary of where marks are allocated by the markscheme, alternative methods and misconceptions.

I did this activity with a Year 12 group whilst reviewing an A-Level paper and it was a such a better use of time. The students were more engaged and I could interact with the class on a much more productive level.

302. Log Proof Puzzle

If you can guess where today’s blog image came from you obviously consume too much damn fine cherry pie and fresh coffee!

log lady

Image credit: Pinterest

You may have guessed that the topic of this post is logs. If you are introducing the rules for adding and subtracting logs or revising them, I have just the resource for you. It’s a basic proof of both rules with a twist. The instructions are in the wrong order and you must rearrange them into the right order.


Are you sure?

For those of you who have a student or two who rush everything and don’t read the instructions there is a sting in the tail. One of the lines of proof is a tiny bit wrong. The methodical student will find it, the one who races through may end up changing more than one line – hence breaking the rules.

Have fun!

Proving log rules for addition and subtraction

Answer: It’s the ‘Log Lady’ from the cult classic ‘Twin Peaks’!

297. Crabby Functions

I take no credit for this ‘aide-memoire’ – it comes from a most delightful and hardworking student. To quote a colleague “She is the poster-child for the benefits hard work”.

Let’s call this student Natasha (not even close to her real name). Natasha had been struggling to work out the difference between graph/function transformations, in particular f(x+a) and f(x)+a. Which way did the graph move? How could you tell? Then she had a brain wave:

She drew little Y shapes on the brackets:

One of the brackets now looks like a little crab:

And we all know crabs move sideways – so it most be a horizontal translation!




Thank you Natasha!

295. I know how to integrate, but which rule to use?

You know that point when you’ve covered the Integration content in A2, the class can do all the different forms and then you set mixed questions … it’s like it’s in a different language. All that wonderful knowledge seeps out like water in a sieve. There must be a help sheet or tool that gives students a starting point, until their confidence and experience grows?

core 4 integration flowchart

Rewind to proving an integration rule. I was discussing a textbook proof of an integration rule with a student and I just didn’t like it. It niggled in my head that I’d been shown a better method when I was first learning this stuff. After a quick dash to the stockroom and a climb up a step ladder, I found a later edition of the textbook I’d used at A-Level. I was right – the Bostock & Chandler proof was far more elegant and comprehensible. Problem solved!

While I had this book out I had a flick through the pages. A flowchart caught my eye – not a fancy infographic, a proper ‘get the flowchart stencil out’ chart. It basically talks students through how to choose an integration strategy. I could have photocopied the page, but it was rubbish quality when I tried. I believe the book is now out of print, so I have recreated the flowchart page with full credit to it’s source. I hope it helps your students as much as it has mine.

C4 Integration flowchart (pdf)

288. Seriously, when am I going to use this?

Oh, that question … heard often from the mouths of those who will not go on to study Maths at a higher level! But when it’s more able students who can’t see the necessity of fundamental principles … Well, that’s a bit worrying.

M’colleague, Mr D, has nailed the answer to this question. When I say ‘nailed’ I obviously mean ‘stuck’ and he has literally* stuck the answer on the wall.
*Note: Mathematician using correct definition of literally.

Here you go:


If you zoom in on this student work, on A2 Differentiation, you can see that he has annotated all the skills used and when you first meet them in the curriculum:


Such a simple idea to tie together seemingly unrelated parts of the Maths curriculum. It also reinforces the need to keep all basic skills sharp.

I’d say it was genius, but then I’d never hear the end of it!