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Homework Help: Line Perpendicular to plane

  1. Apr 8, 2008 #1
    1. The problem statement, all variables and given/known data

    Find the line ... . Show that it is perpendicular to the plane A and find the angle that the line makes with the plane B

    2. Relevant equations

    3. The attempt at a solution

    I've found the line, but how do I go about showing it's perpendicular and finding the angle?
  2. jcsd
  3. Apr 8, 2008 #2
    The plane must be in either of the two forms.. either it's in a vector form, or Cartesian form. Let's say, it's in a cartesian form..

    Ax + By + Cz + D = 0

    So you have the direction ratios of the normal to the plane. for a line to be perpendicular to this, you need to get the direction ratios of the line as well. Once you have that, use the check for perpendicularity:

    l_1 l_2 + m_1 m_2 + n_1 n_2 = 0

    which is equivalent to checking if the dot product of the two vectors is zero or not, which i'd say is a better method.

    For finding the angle, find a line parallel to the given line [using the direction ratios] and do the same thing for the plane's normal.. and then use the formula:

    \cos{(\theta)} = \frac{\overrightarrow{a}~.~\overrightarrow{b}}{|\overrightarrow{a}||\overrightarrow{b}|}
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