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- From: alopez-o@neumann.uwaterloo.ca (Alex Lopez-Ortiz)
- Subject: sci.math FAQ: Surface Area of Sphere
- Summary: Part 35 of many, New version,
- Originator: alopez-o@neumann.uwaterloo.ca
- Message-ID: <DI76nI.EC1@undergrad.math.uwaterloo.ca>
- Sender: news@undergrad.math.uwaterloo.ca (news spool owner)
- Approved: news-answers-request@MIT.Edu
- Date: Fri, 17 Nov 1995 17:16:30 GMT
- Expires: Fri, 8 Dec 1995 09:55:55 GMT
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- Xref: senator-bedfellow.mit.edu sci.math:124753 sci.answers:3468 news.answers:58011
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- Archive-Name: sci-math-faq/surfaceSphere
- Last-modified: December 8, 1994
- Version: 6.2
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- Formula for the Surface Area of a sphere in Euclidean N -Space
-
-
-
- This is equivalent to the volume of the N -1 solid which comprises the
- boundary of an N -Sphere.
-
- The volume of a ball is the easiest formula to remember: It's r^N
- (pi^(N/2))/((N/2)!) . The only hard part is taking the factorial of a
- half-integer. The real definition is that x! = Gamma (x + 1) , but if
- you want a formula, it's:
-
- (1/2 + n)! = sqrt(pi) ((2n + 2)!)/((n + 1)!4^(n + 1)) To get the
- surface area, you just differentiate to get N (pi^(N/2))/((N/2)!)r^(N
- - 1) .
-
- There is a clever way to obtain this formula using Gaussian integrals.
- First, we note that the integral over the line of e^(-x^2) is sqrt(pi)
- . Therefore the integral over N -space of e^(-x_1^2 - x_2^2 - ... -
- x_N^2) is sqrt(pi)^n . Now we change to spherical coordinates. We get
- the integral from 0 to infinity of Vr^(N - 1)e^(-r^2) , where V is the
- surface volume of a sphere. Integrate by parts repeatedly to get the
- desired formula.
-
- It is possible to derive the volume of the sphere from ``first
- principles''.
-
-
- _________________________________________________________________
-
-
-
- alopez-o@barrow.uwaterloo.ca
- Tue Apr 04 17:26:57 EDT 1995
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