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Homework Help: Vector Problem

  1. Nov 7, 2009 #1
    1. The problem statement, all variables and given/known data

    A vertical building was built on a horizontal plane. The plane is then tilted to A=(0,0,0) B=(1,2,0) and C=(0,3,1). By what angle (in radians) does the building now deviate from the vertical?


    2. Relevant equations

    Dot Product
    Cross Product

    3. The attempt at a solution

    So what I did was take the cross product of the B and C, relative to A.

    BxC = |2 0|, |1 0|, |1 2| = (2, -1, 3)
    ........|3 1|, -|0 1|, |0 3|

    Now this is the part where I dont know what to do.

    I took the Dot product of (BxC) with (0, 1, 0)

    theta = arccos (u.v)/(|u||v|) = (-1/[tex]\sqrt{}14[/tex][tex]\sqrt{}1[/tex])

    and i got an angle to be 1.84 in radians, which was wrong. I dont know what the answer is, I'm using webwork
    So if anyone can help me, that would be great.

    Thanks
     
  2. jcsd
  3. Nov 7, 2009 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    Why do you think the vertical direction is (0,1,0)? My guess would have been that they meant it to be (0,0,1).
     
  4. Nov 8, 2009 #3
    Your Right! I must of been thinking in 2D..
    Thank You Dick!!
     
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