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Homework Help: Body Diagonals of a cube

  1. Sep 1, 2006 #1
    Can anyone out there tell me what the body diagonals of a cube are.
    I am asked to find the angle between the body diagonals of a cube. Seeing as how it is just the application of the dot product it does not seem difficult other than I do not know what body diagonals are (I have an idea but would like to know from someone for sure).
     
  2. jcsd
  3. Sep 1, 2006 #2
    Found it! The body diagonals of a cube are the from one point on a cube to the next and the angle between them is 90 degrees (they bisect one another)
    Should of looked first
     
  4. Jan 11, 2007 #3
    I have the same problem, yet, I still can't picture it.
     
  5. Jan 11, 2007 #4
    slice the cube through the intersecting diagonal... the shape that is left is like an "incline plane". or imagine a table with square top, and square sides and square base with the legs intersecting.
     
  6. Jan 11, 2007 #5

    Gokul43201

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    Last edited by a moderator: Apr 22, 2017
  7. Jan 11, 2007 #6
    I seem to be getting an answer of 45 degrees which isn't right...
     
  8. Jan 11, 2007 #7
    When drawing the vectors in the case within the cube, do they have to be from the same origin?
     
  9. Jan 11, 2007 #8
    nvm, thx for your help~!
     
  10. Jan 11, 2007 #9

    Gokul43201

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    Did you get the correct answer?
     
  11. Jan 11, 2007 #10
    i used a unit cube.
    with one diagonal at (0 0 1) (1 1 0)
    the other diagonal at (0 0 0) (1 1 1)
    but it doesn't work, hmmm...for a sec i thought i did get it.
     
  12. Jan 12, 2007 #11

    Gokul43201

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    Good, now find the vectors describing the diagonals using the vectors given above, representing their end-points.

    What do you mean by "it doesn't work"? What doesn't work?

    The answer written by Disar is incorrect.
     
  13. Jan 12, 2007 #12
    oh, if that's the case, I think I got it LOL Thanks a bunch!
     
  14. Jan 12, 2009 #13
    I went to my professor about this problem and he told me to use A=x+y+z and B= -x+y+z, naming one of the body diagonals A, and the other body diagonal B. I'm a bit confused how to take the 4 points above to make them fit the A and B my prof gave me. Can anyone help me with this please?? Thanks
     
  15. Sep 29, 2009 #14
    Can you help me? I still dont get it, thanks
     
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