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Math Help - Unit Vector oeroendicular to a plane

  1. #1
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    Unit Vector oeroendicular to a plane

    guys please help me with this problem:

    Find a unit vector perpendicular to plane PQR determined by the points P(3,-3,-1), Q(2,1,-1), and R(2,-2,-1)
    the book says the answer is :
    (+-)(2/3i +2/3j+1/3K)
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  2. #2
    MHF Contributor Calculus26's Avatar
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    Let u be the vector from P to Q and v be the vector from Q to R

    Then N = u x v

    the unit normal is (u x v)/|u x v|
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  3. #3
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    couldnot find the answer

    i tried that way but still getting different answer than the book
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  4. #4
    MHF Contributor Calculus26's Avatar
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    Check the coordinates of the given points but with the pts you gave:

    u = -i + 4 j (P to Q) v = -3 j ( Q to R)

    u x v = k
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