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Vector addition etc

  1. Mar 15, 2009 #1
    1. The problem statement, all variables and given/known data
    Find the angle between the following vectors?
    A = -2.00i^ + 6.00j^ and B = 2.00i^ - 3.00j^ (the ^ means 'i hat')



    2. Relevant equations
    Theta = tan^-1 = (opposite/adjacent)


    3. The attempt at a solution
    i said for the first part of the component that
    theta(A) = tan^1 (6/2) = 71.57
    and then did the same for the other component
    theta(B) = tan^1 (2/3) = 33.70

    and the angle between them should be the addition of those two? ie 105.27?
    im confused...this doesnt look right
     
  2. jcsd
  3. Mar 15, 2009 #2
    Have you done dot or cross products yet? If you have the easiest way to compute the angle is through the association that

    [tex]\mathbf{A}\cdot\mathbf{B}=|\mathbf{A}||\mathbf{B}|\cos{\theta}[/tex]

    or with cross products

    [tex]|\mathbf{A}\times\mathbf{B}|=|\mathbf{A}||\mathbf{B}|\sin{\theta}[/tex]

    where [itex]\theta[/itex] is the angle in between them.
     
  4. Mar 15, 2009 #3
    nope, ive never seen that before?
     
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