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Homework Help: Find a vector parallel to two planes

  1. Jan 29, 2006 #1
    there are two planes:

    3x+y+z=1
    3x+z=0

    find a vector U with positive first coordinate that is parallel to both planes.

    the way I went about solving this:
    the normal vectors are: <3,1,1> and <3,0,1>, the cross product of the vectors will give a vector perpendicular to the normal, which means it would be parallel to the two planes right?
     
  2. jcsd
  3. Jan 29, 2006 #2

    0rthodontist

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    Yes, that's right.
     
  4. Jan 29, 2006 #3
    when I did this, I get <1,0,-3> and this is not correct. so i do not know where I went wrong
     
  5. Jan 29, 2006 #4

    0rthodontist

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    (1, 0, -3) is correct. Maybe you are comparing it to a vector that is a multiple of (1, 0, -3)--there is more than one answer. (2, 0, -6) is also correct.
     
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