As someone associated with the Tauists (a Times editorial described me as a leader of a maverick band of mathematicians promoting tau) I shouldn’t be celebrating Pi Day today. But Tauists and Piists can live in peace as the following link shows (and from which the above picture is taken): http://mitadmissions.org/blogs/entry/i-have-smashing-news Now, if you’ll excuse me I need to rush off to give a talk about card cheating in a local school and then go to Durham for a Yorkshire Durham Geometry Day celebrating the life of Tom...

## Recipe for Pi Day

posted by Kevin Houston

International Pi Day is approaching (14th March) and the world is looking for exciting recipes for pies to celebrate such an important date in the calendar. Well, here’s a great idea. They are called “Tau-nados”. In order to get the pun one has to pronounce tau in the English way (“tor”) rather than the American way (sounds like cow). The idea is that you get two pies in one – hence the tau from 2 pi. And not only that the pies are twisted to form a double helix! See the website http://www.instructables.com/id/Tau-nados/ for the recipe. Here’s a taster of what they look like: Thanks to Joseph Lindenberg for bringing this to my...

## Pi is 4 video

posted by Kevin Houston

I mentioned the “proof” of π=4 in a previous post. In time for Pi Day on Monday, I’ve created a new video setting out the problem. For those not inclined to view videos here is the problem: Take a circle of diameter 1. Its circumference is π since its radius is 1/2 and a circumference is 2π times radius. Now put a square round it. The length of the perimeter of the square is 4 since each side has length equal to the diameter of the circle. Now fold in the corners like so. Since there was no stretching or shrinking, the length of this new curve is also 4. Do the process again, i.e., fold in all the corners. The length of this curve is still 4 since no stretching or shrinking was involved. Do it again. The length is again 4. We can take the limit of this process. The limit is a circle. Since the jagged curve gets closer and closer to the circle and always has length 4 we can see that the perimeter of the circle has length 4. But the perimeter length is also equal to π. Therefore, π is 4. Where is the...