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(19 Posts)
irvineoneohone Wed 19-Apr-17 13:27:04

What is it?
I know it is 3.14159.... and the ratio of a circle's circumference to its diameter, etc.

But what is it really?
My ds asked me, and I couldn't really answer that properly. Is there any resources that explains what it is?

GattoColorCioccolatto Wed 19-Apr-17 13:31:20

YouTube is your friend.

GertrudeBelle Wed 19-Apr-17 13:35:33


noblegiraffe Wed 19-Apr-17 13:40:04

The ratio of a circle's circumference to its diameter is what defines pi.

If you take any circle, no matter how big (solar system sized!) or small (atom sized!) and divide its circumference by its diameter, you will always get 3.141592653..... which is pretty astounding.

Pi crops up in lots of formulae involving circles or curves.

Cagliostro Wed 19-Apr-17 13:40:15

One of my pupils asked about pi recently and we cut string to the length of the diameter of a circle and then used that to measure the circumference. Did that with lots of different circles to show that we always needed 3.14 x the diameter length.

prh47bridge Wed 19-Apr-17 13:40:30

It is the ratio of a circle's circumference to its diameter. That is how it is defined. That is what it really is.

It happens to be an irrational number which means it cannot be expressed precisely as a decimal or as a fraction. 22/7 is close but is not bang on. Many people find it hard to get to grips with the idea that irrational numbers exist but there is a simple proof.

FatCatFaces Wed 19-Apr-17 13:41:50

It's a never-ending number with no pattern.

irvineoneohone Wed 19-Apr-17 13:45:32

Thank you, I've watched few you tube and found good one.(why didn't I think about that...)

I'll do what Cagliostro did as well. Great idea.

Thanks everyone!

pincha Wed 19-Apr-17 13:46:04

It is what it is, what you've said in your OP.

Not sure what else you're looking for?

irvineoneohone Wed 19-Apr-17 13:50:37

pincha, I know!
But what I needed was something like Cagliostro's suggestion.
So, I might sound really thick, but glad I asked! grin

Cagliostro Wed 19-Apr-17 14:00:35

Oh I can't take credit for it BTW I think I saw it on Facebook grin blush

Wheredidallthejaffacakesgo Wed 19-Apr-17 21:28:34

It's not simply irrational (like your common or garden root 2), it's actually transcendental.

It is a thing of wonder and beauty, and best of all e^(pi*i)+1=0

irvineoneohone Wed 19-Apr-17 21:51:00

Yes, Wheredid, that's what I really wanted to explain to my ds.
He knows what it is, he knows how to use it, but that's all.
But he started questioning what it really was, so I really wanted to give him some answers.
I will keep researching!

Wheredidallthejaffacakesgo Wed 19-Apr-17 22:32:34

Tell him he won't really and truly understand the secrets of pi until he undertakes graduate level study in mathematics. I would recommend the Cambridge Master of Advanced Studies in Mathematics course (aka Part III of the Tripos).

irvineoneohone Wed 19-Apr-17 22:42:57

Long way to go, but thank you.
It makes me happy that he gets interested in something, but sad at the same time I can't really help him.
I guess he need to pursue it himself in the future.

scaevola Wed 19-Apr-17 22:44:52

Pi, you say....

irvineoneohone Wed 19-Apr-17 22:48:36

Yes, my ds is a geeky and quirky child, but fortunately, he has friends!grin

JustRichmal Thu 20-Apr-17 09:36:21

I think this is a really interesting question and, if nothing else, shows he is thinking about what he is taught, not just taking it as given.

I would like to know the answer, but have not the time to take a Cambridge Masters degree, even if I could pass the entrance test!

Numberphiles usually has some quite good youtube videos.

I would love also to know about the number e. Again, I sort of get the idea of a function with a gradient at any point being whatever the value of y is, but do not quite see why it works. Also why does e crop up again in binomial expansion?

irvineoneohone Thu 20-Apr-17 16:28:12

Thank you Richmal, Numberphiles looks great.
We will have lot's of fun watching them! smile

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