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Homework Help: Intersection of 2 planes

  1. Mar 6, 2008 #1
    1. The problem statement, all variables and given/known data

    True or False: The intersection of two planes in R3 is always a line.

    3. The attempt at a solution

    I'm pretty sure that this statement is true because two planes can only be parallel, or they must intersect in a line because the are infinate.

    But I have no ideas on how to prove this mathematically. Any ideas?
  2. jcsd
  3. Mar 6, 2008 #2
    Are you familiar with the cross product? If so, consider the cross product of the normals to each plane.

    By the way, what if the planes are parallel?
    Last edited: Mar 6, 2008
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