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Homework Help: Finding z coord. drection angle given x and y coord. direction angle

  1. Sep 17, 2013 #1
    1. The problem statement, all variables and given/known data
    The x and y coordinate direction angles of a vector are 50 and 105 degrees, respectively. If the z component of the vector points in the negative z direction, what is the z coordinate direction angle?

    2. Relevant equations

    3. The attempt at a solution
    I was going to try using cos^-1(z comp/magnitude) but since I'm not given a specific vector, that wouldn't work..
    Can someone kind of explain how to go about solving this? I feel like it's easy and I'm making it complicated.
    Much appreciated!
  2. jcsd
  3. Sep 17, 2013 #2


    Staff: Mentor

    If your vector is ##\vec{u}##, then ##\hat{u} = \frac{\vec{u}}{|\vec{u}|}## is a unit vector. From this you can get the length of the z-component and the angle the z-component makes with the z-axis.
  4. Sep 18, 2013 #3
    I don't really understand what you mean. how would I solve for the vector without having any values to work with?
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