Talk:Octahedron

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[edit] Octahedron equation

¿Shouldnt be on the article the equation of the octahedron?

  • Which is:
    • for the volume |x|+|y|+|z| \le k
    • for the surface | x | + | y | + | z | = k
  • where k \in R

[edit] Andreini Tessellations

This article says there are 5 Andreini tessellations, but the article Andreini tessellation says there are 28. Which is correct? --Auximines 13:14, 21 Apr 2004 (UTC)

Maybe someone meant to say that five (would you believe six?) of the 28 contain octahedra. —Tamfang 06:53, 25 November 2006 (UTC)

[edit] New stat table

I replace stat table with template version, which uses tricky nested templates as a "database" which allows the same data to be reformatted into multiple locations and formats. See here for more details: User:Tomruen/polyhedron_db_testing

Tom Ruen 00:53, 4 March 2006 (UTC)

[edit] volume

i really need to know how i would get the formula that is given for the volume of the octahedron.... like.. the working out to get the formula...

PLEASE, THANKYOU

-Dave —Preceding unsigned comment added by 58.169.29.65 (talk • contribs) 17:39, 9 October 2006

Well, let's see. Starting with the octahedron whose vertices are (0,0,±1) etc., consider the "first octant", that portion in which x,y,z are all positive. That's a (skew) pyramid whose base is a right triangle. A pyramid's volume is (height)×(area of base)/3; the base is half of a unit square, and the height is 1, so the pyramid's volume is 1/6. There are eight such pyramids, so the total volume is 8/6 = 4/3. But it's usual to express volume in terms of the edge length, and this octahedron has edge √2; so we divide 4/3 by the cube of √2 and get (√2)/3 for the volume of an octahedron of unit edge. I didn't look at the answer while deriving this, so now I will — ah, good. ;) —Tamfang 04:52, 11 October 2006 (UTC)

[edit] hexagonal prism

I changed the hexagonal prism from 6 triangle to 6 squares. To the best of my knowledge, that is how a hexagonal prism is constructed. Change it back if I was in error. Scott MacHardy 02:35, 23 October 2006 (UTC)

Everyone makes mistakes! —Tamfang 04:14, 28 October 2006 (UTC)

[edit] Alum

The substance Alum is generally octahedral i beleive (at least, mine always is). Perhapse it should be mentioned somewhere? 71.28.13.158 03:35, 28 November 2006 (UTC)

[edit] subgroups

It occurs to me that the subgroups of Oh include Th as well as Td. Is there a figure that we can associate with that subgroup? —Tamfang 22:56, 25 April 2007 (UTC)