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Homework Help: Unit vector orthogonal to plane

  1. Jan 30, 2012 #1
    1. The problem statement, all variables and given/known data

    Find a unit vector with positive first coordinate that is orthogonal to the plane through the points P = (-4, 5, 4), Q = (-1, 8, 7), and R = (-1, 8, 8).

    2. Relevant equations

    u = PQ = Q - P
    v = PR = R - P
    ans = uXv = PQ X PR

    3. The attempt at a solution

    so I did:
    PQ = Q - P = (3,3,3)
    PR = R - P = (3,3,4)

    Then I computed the cross product to get the answer.

    |i..j..k|
    |3 3 3| = <(12-9) , -(12-9) , (9-9)> = <3, -3, 0>
    |3 3 4|

    The 0 is correct but the 3 and -3 are not. What am I doing wrong?
    Thanks!
     
  2. jcsd
  3. Jan 30, 2012 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    welcome to pf!

    hi olivia! welcome to pf! :smile:
    not a unit vector? :wink:
     
  4. Jan 30, 2012 #3
    ohhhh haha thank you so much!
     
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