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I faced one interview last week. In that interview, the interviewer asked a very basic question; but, it was out of my knowledge. He wanted to check my very basic mathematical skills, and wanted to see whether I am fond of mathematics or not.

The question was, what is pi?

The only thing I know of pi is that it equals $3.14$.

So, what is pi? From where this constant come? Why is the value $3.14$? As well as any other related questions that walk around this term "pi".

Waiting for your kind reply.

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In fact, pie is something delicious. For questions about the number $\pi$ (which does not equal $3.14$) cf. math.stackexchange.com/questions/400369/…, math.stackexchange.com/questions/53023/… o rsimply en.wikipedia.org/wiki/Pi –  Hagen von Eitzen Jun 8 '13 at 7:41
    
It is "PI" not "PIE" for the case the next time it rises as question in a written exam. –  al-Hwarizmi Jun 8 '13 at 8:03
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None of the previous tags were appropriate. Jeez... –  J. M. Jun 9 '13 at 16:12
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closed as not a real question by fpqc, O.L., Jonas Meyer, Marc van Leeuwen, Amzoti Jun 8 '13 at 7:59

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

2 Answers

Pi

It is the ratio of a circle's circumference to its diameter. However it is an irrational number (i.e. if you sit down to list down all its digits you will have to go on and on) and is approximately equal to 3.14159.

Pi as continued fractions:

$$\pi = \cfrac{4}{1+\cfrac{1^{2}}{2+\cfrac{3^{2}}{2+\cfrac{5^{2}}{\ddots}}}}$$

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@shwawata: Did you make that picture? –  Jonas Meyer Jun 8 '13 at 8:07
    
@shaswata Thanks for explaining this. But I didn't understand this continued fraction. Can you explain me this, please ? –  devnull Jun 8 '13 at 9:53
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First of all, it's just "pi", there is no letter e on the end. This is the name of a greek letter. As for what it is, the most basic definition is the ratio of the circumference a circle to its diameter. Of course there are many applications and alternative ways of calculating pi, but I would say that this is the most fundamental definition.

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