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### Course: Math for fun and glory>Unit 1

Lesson 4: About pi and tau

# Pi is (still) wrong

Please excuse the simple math and spelling errors. You shouldn't believe anything I say without double-checking even at the best of times. Go here: http://tauday.com/ and here: http://www.math.utah.edu/~palais/pi.html Me: http://vihart.com. Created by Vi Hart.

## Want to join the conversation?

• If radians are so great why do we spend our whole time in elementary school using degrees?
• As far as I know, 360 comes from the fact that the base of the Sumerian nummerical system is 60.
• If tau is so great didn't my math teacher doesn't know about tau? ):
• B-cause some people don't have the weight or the audacity to learn about tau till college. I've heard some college professors have no idea what tau is ;-)!
• Dose that mean pi r 2 would be 1/2 tau r 2?
• That's right. Written that way, it's pretty easy to imagine that that would be the formula for the area of a circle. Think of the circle as being a regular polygon with n sides for some very large n, and draw line segments from the center to each of the vertices. The area of all of those triangles put together is n times 1/2 times the base times the height of each of the triangles, or 1/2 times (n times the base) times the height. Well, the height is obviously r and n times the base of the triangle is very close to the circumference of the triangle, which is tau r, so the area is 1/2 tau r squared. Pretty easy proof when you use tau, isn't it?
• why did people call π, pi?
• π is called π because the Greek word for "circumference" is περιφέρια (when you pronounce it, it sounds like per-ee-FAIR-ee-a), and π is the first letter of that.
• so how is pi wrong? is it just really complex?
• As she says in the video, its not mathematically wrong. It is just counter-intuitively defined.

The entire Tau movement basically boils down to "Why should we use an unintuitive value when its so easy to define an intuitive one (namely Tau = 2 pi)?"

They do to some extent have a point, but they are fighting centuries (millenium?) of tradition.
• Which is tastier? Pi or Tau?
• Tau, why? Pi is tasty, but 2 Pi is even tastier. Yea for Tau!! 2 Pi or not 2 Pi, that is the question.
• Will schools get rid of the idea of Pi and support Tau?
• Who can guess? There is a lot of institutional resistance in the form of textbooks and calculators and current lesson plans and everyone who learned pi who don't want to give that up. But societies are capable of making tremendous change when they feel that it's worth it. If there was a sustained body of research that showed that trigonometry and calculus were significantly easier to comprehend with a more intuitive circle constant, then I do think there would be some action.