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### Happy π Day!

Posted: **Sun Mar 14, 2010 8:49 am**

by **Sam**

This 14th day of march, 3.14, makes it pi day. π is a very special number mathematics and trigonometry.

Circumference of a circle is a function of π times twice the radius:

C(r) = 2πr

What's cool about this, is that the concept of radian measures come from this, where 360°≡ 2π (is equivalent to) on a unit circle. Degrees are units that basically come from nowhere, I mean who's to say that a full circle has to be 360 degrees? Radian measures are actual measured numbers, making them more usable within equations.

Euler's Identity:

e^(π*i) = -1

My friend showed me this last one, I thought it was cool.

Today is the day you can be mathematically irrational. (and eat pi*e)

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 10:48 am**

by **le-em**

This is so cool, a π day. Anyway, the person I sit next to in Math is crazy about π.

Happy π Day

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 12:14 pm**

by **Brf**

There is a very simple formula that converges to pi:

4 * ( 1/1 - 1/3 + 1/5 - 1/7 .....)

alternating plus and minus, with reciprocal of the odd numbers. It converges very slowly, but if you take the average of the last two terms you are working on, it converges alot faster.

### why 14th March itself is selected as phi day

Posted: **Sun Mar 14, 2010 12:41 pm**

by **pratish7**

Why 14th March itself is selected as phi day

Is there any story behind it

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 1:12 pm**

by **Shadow of Nobody**

Third month of the year, 14th day? 3/14 = 3.14. That' my *guess*, anyway.

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 1:56 pm**

by **stickerboy**

Happy π Day ^_^

Think I'll go have me some π for dinner

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 2:52 pm**

by **Claritty**

My math teacher is probebly very excited about this.

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 4:36 pm**

by **jbones**

Well happy π day to you too. clever

So, I think I'll make an apple π to celebrate the spirit of the π day.

And a fine

**π** to everyone.

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 7:49 pm**

by **god0fgod**

That Euler's identity looks complicated.

I've recently memorised pi to 15 digits. It wasn't because I was sad, I just wanted to test out the

method of loci. I'll be looking at this peg system next.

### Re: Happy π Day!

Posted: **Sun Mar 14, 2010 7:59 pm**

by **Desdenova**

Just remember this, though:

pie = 8.53973422

pi = 3.14159265

### Re: Happy π Day!

Posted: **Mon Mar 15, 2010 3:10 am**

by **bonelifer**

either way π is yummy.

### Re: Happy π Day!

Posted: **Mon Mar 15, 2010 6:55 am**

by **Phil**

god0fgod wrote:That Euler's identity looks complicated.

It's not terribly difficult to derive, nor is it useful for anything other than verifying trigonometric identities (particularly the double angle ones), though itself is the product of one; it's just considered one of the more "beautiful" mathematical proofs as it contains the 3 basic arithmetic operations (when written as e^(π*i) + 1 = 0) --

wiki has a section on it actually.

### Re: Happy π Day!

Posted: **Mon Mar 15, 2010 3:47 pm**

by **god0fgod**

For a start I don't know much about imaginary numbers. While I know they are square roots of negative numbers I don't know how they are used.

### Re: Happy π Day!

Posted: **Mon Mar 15, 2010 6:53 pm**

by **Darth Wong**

god0fgod wrote:For a start I don't know much about imaginary numbers. While I know they are square roots of negative numbers I don't know how they are used.

They are used in electrical engineering, as a way of conceptualizing phased voltage/current waveforms. It's been 20 years since I did that myself though, so I can't give you much more in the way of detail.

### Re: why 14th March itself is selected as phi day

Posted: **Mon Mar 15, 2010 8:47 pm**

by **Tom**

pratish7 wrote:Why 14th March itself is selected as phi day

Is there any story behind it

Shadow of Nobody wrote:Third month of the year, 14th day? 3/14 = 3.14. That' my *guess*, anyway.

That's correct. It seems pretty obvious to me, but it may not seem so obvious for those who are used to seeing dates written in dd.mm.yy format where Pi Day would look like 14.3.xx instead of 3.14.xx.