# Talk:Circumference

## Definition of pi

When the formula for circumference is mentioned, first 2πr should come, and later should πd be derived. Reason being that if we consider the circle itself as an arc, it subtends 360° or 2π radians, and the apothem being r, the formula is 2πr. —Preceding unsigned comment added by 120.62.174.37 (talk) 15:49, 21 August 2010 (UTC)

- The definition of Pi is the ratio between circumference and diameter. It therefore makes sense to quote πd first, and then the derived 2πr afterwards. [In future when you are posting a new comment to a talk page, please add it to the foot of the page, not to the top. Please remember also to sign your comment by typing 4 tildes ~~~~ or using the signature button on the edit pane.] David Biddulph (talk) 16:00, 21 August 2010 (UTC)

I edited this page I added how to find the circumference of an oval can someone tell me how to make a link so when someone types in to search "circumference of an oval" it shows up on search results PLEASE--Whats inside the light bulb? (talk) 03:20, 2 January 2010 (UTC)

Let us see a proof that a circle's circumference is of finite length and can be measured. --User:Juuitchan

- Logic will do to tell you that it is of finite length, logic will also tell you that it will be of inifinite detail. You can use the approximation by polygones to prove both things... BrunoX 01:13, 22 October 2006 (UTC)

- I agree. --User: mkomnipotens

- The first paragraph in this article uses some integral calculus to prove that the circumference of a circle is 2πr. I suppose that was intended to satisfy User:Juuitchan, who requested a proof that the circumference is of finite length, but is any of this
*important*for this Wikipedia article? The symbol π is*by definition*the ratio of the circumference of a circle to its diameter, so the result is trivial at best. Why confuse our readers with the heavy machinery? — Aetheling (talk) 20:07, 18 December 2007 (UTC)

- I agree, the integral calculus in this definition of the circumference of a circle is pointless, in my opinion (and I'm a maths graduate). Contrast the entry for [pi] where [pi] is explicitly defined as being the ratio of the circumference to the diameter. Given that, you dont need anything else to explain the definition. Another minor point is that the formula refers to "r" but does not define what "r" is (yes, most people know what it is but how would you find out from this article?). But that's irrelevant as the calculation involving the integral should be removed and is verging on vandalism IanB (talk) 12:36, 12 December 2008 (UTC).

- That may be because a vandalism from
wasn't fully reverted(look now). 15:40, 12 December 2008 (UTC)**18:33, 26 November 2008**- I'm not yet fully convinced. I agree the integral now makes more sense, and you've defined r as the radius, and it's an interesting calculation. But the text says the formula is being derived without reference to the definition of π. Yet you are relying on the knowledge that arcsin(1) is π/2. IanB (talk) 23:22, 19 December 2008 (UTC).

- That may be because a vandalism from

## Merge

Should Circumference be merged with Perimeter. As a non-genius I vote no. The reason is because I feel that most people can be confused with just the title Perimeter. When I search for info about a circle, to help with problem solving in school work, I don't think of Perimeter I think of Circumference. I'm sure there's lots of reasons why you two people above think otherwise with tons of formulas to prove your point. But I am a simple minded person and prefer my searchable topics to be simple also. *CIRC*le sounds like *CIRC*umference, see thats easy for me to remember, especially with my short-term memory. Thanks for listening to my input.

**NO**this articled shouldn't be merged with Perimeter. I think Circumference is a quite exceptional and particular case of a perimeter and it's worth of its own article. BrunoX 01:47, 22 October 2006 (UTC)

- I don't know much about anything in this article, but do you care to say
*why*the articles should not be merged? To most people, including me, the two topics are extremely similar, however, I'll remain neutral in the discussion. But if you really don't want the articles to be merged you should put down some more reasons.**CattleGirl**^{ talk}07:47, 23 October 2006 (UTC)

- I don't know much about anything in this article, but do you care to say

I vote no. Not knowing what a circumference was, i found the answer immediately, and was happy about that. I think it is good to keep the two articles apart and link between them as is done now. Short articles which go straight to the point are more helpful than long articles where you have to really search for the information you are looking for.

NO. Circumference is a perimeter, but a perimeter is not necessarily a circumference. They are different enough to warrant separate articles, in my opinion. CattleGirl - your logic leaves much to be desired. This is something that would change the status quo. Therefore, how about this: Provide more reasons why these articles SHOULD be merged! Jeremy 71.134.190.99 19:48, 29 November 2006 (UTC)

## Long Pages?

Why is this at the top of Special:Longpages? **TheThingy** ^{Talk} 18:18, 10 June 2007 (UTC)

- Because someone thought he was clever to vandalise it. Jackaranga 23:38, 10 June 2007 (UTC)

## Non mathematical definitions

Would it be possible for somebody suitably equipped (not me!) to provide definitions of Circumference other than the mathematical definition? The page is entirely unhelpful within the context of other (non-mathematical) Wiki articles referring to the circumference of a thing. --Te Irirangi 01:33, 4 October 2007 (UTC)

I agree. Sure, a maths professor or someone like that would get this straight away, but when I showed my maths teacher Circumferance on Wikipedia and he didn't have a clue. What does this Pi=Sin=Tan=Square root of 1+X^{2 } rubbish mean anyway? Koshoes (talk) 21:34, 3 January 2009 (UTC)

## External Links

I deleted a link to a Friendster profile in the Links section.

Too ridiculous. 76.235.74.105 (talk) 21:49, 21 January 2008 (UTC)

## Definition of a circumference.

It looks strange to define circumference as a distance (length of a "line segment") on a curved line; according to that definition, the circumference will rather be the perimeter of an inscribed polygon --Chiloa (talk) 13:33, 4 August 2008 (UTC)

## Error in Ramanujan-1914 #2 for perimeter of an ellipse?

Hello, I believe there is an error in Ramanujan-1914 #2 for the perimeter of an ellipse. Should the 1/2 at the beginning of the expression be a pi instead? Setting a=b (a circle) gives the perimeter approximately equal to a or b (clearly not even close). Dave of Indiana 67.237.34.16 (talk) 03:43, 22 November 2008 (UTC)

- Whoops, no, it
equal between**should***a*and*b*——pi is a separate factor of*c*(someone erroneously added it to #1, which I've corrected). ~Kaimbridge~ (talk) 15:11, 22 November 2008 (UTC)

Now I'm confused. All other references that I can find of Ramanujan's equations for the perimeter of an ellipse have a pi instead of a 1/2. If a=b and the factor is pi then the perimeter equals pi*2*a -as expected. If a=b and the factor is 1/2 then the perimeter equals a -which is clearly incorrect. Am I missing something? 67.237.34.16 (talk) 21:22, 22 November 2008 (UTC)Dave of Indiana

- Yes, but what is presented right there is just the perimetric
**radius**,*Pr*, not the circumference, which is presented earier:- ~Kaimbridge~ (talk) 21:51, 22 November 2008 (UTC)

Got it now. Thanks for clearing that up. I took Pr to be the Perimeter. That's what I get for not reading the whole article. :) Dave of Indiana67.237.34.16 (talk) 00:32, 23 November 2008 (UTC)

## Circular argument

As stated above: Yet you are relying on the knowledge that arcsin(1) is π/2. IanB (talk) 23:22, 19 December 2008 (UTC). Since arcsin(1) is by definition a quarter circle, this means that you are relying on the knowledge that a full circle is 2π, which is what you are trying to prove. This invalidates the entire argument in the first paragraph, which should be deleted. Ehrenkater (talk) 14:08, 29 May 2009 (UTC)

## Modified section Relationship with Pi, added Circle illustration with radius.

I hope other editors will agree with this clean up and addition. Reddwarf2956 (talk) 03:51, 21 August 2012 (UTC)

## please insert link to UMFANG (german wiki)

thx, Gerald Trost — Preceding unsigned comment added by 80.109.227.56 (talk) 03:08, 11 June 2013 (UTC)

## please insert link to UMFANG (german wiki)

UMFANG is linked with perimeter, not with circumference is perimeter a synonym for circumference? somehow UMFANG and circumference should be linked to better find your way from german to english and vice versa. thx, Gerald Trost — Preceding unsigned comment added by 80.109.227.56 (talk) 03:12, 11 June 2013 (UTC)

## citation needed span

The "citation needed span" does not fit well because the span should also include the next sentence, and which does state a few examples of each subject. If you want something else, I am sure we can find/add something. I mean period of sine, cosine and pendulum and brads use the constant in robotics. Simple harmonic motion is another use which is involve with all of the subjects stated. If you feel that the sentences need to be rewrote feel free to give it a try. John W. Nicholson (talk) 00:54, 23 June 2013 (UTC)