# March, 2012

## Free for all Friday

It's that time of the week again! What's been on your mind? What's giving you a headache? As always, drop your questions in the comments box and I'll get back to you as swiftly as I can!

## Quotable maths: Bohr

We all agree that your theory is crazy, but is it crazy enough? - Niels Bohr

## What is a circle? (and how do you answer C2 questions about it?)

A conjecture both deep and profound Needs a proof that the circle is round. In a paper by Erdős Written in Kurdish A counter-example is found. One of my favourite questions to ask students is "what's a circle?" because I get to play "so that means this is a circle!"

## Secrets of the mathematical ninja: Divisibility tricks

Some of the secrets of the mathematical ninja are pretty pointless, when you come down to it: after all, we have machines for most of these things. The divisibility tricks are useful (as far as I can see) only in a very specific circumstance: when you're deciding whether to cancel

## Free for all Friday

It's that time of the week again! What's been on your mind? What's giving you a headache? As always, drop your questions in the comments box and I'll get back to you as swiftly as I can!

## Where to start when you don't know where to start

Right! That's it. I'm mad as hell and I'm not going to take it any more. If one more student looks at a question and says "I don't know where to start!" I'm going to... I'm going to... I'm going to FROWN and look at them VERY CROSSLY. Because I

## Secrets of the Mathematical Ninja: squares near 50.

Difficulty: ** Impressiveness: **** (Many thanks to Swar for pointing me at this one - and challenging me to explain it well!) It's surprisingly easy to square numbers near 50. Here's the recipe: 1. Find the difference between your number and 50. (If you're looking at 46, it'd be -4.

## Free for all Friday

It's that time of the week again! What's been on your mind? What's giving you a headache? As always, drop your questions in the comments box and I'll get back to you as swiftly as I can!