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Homework Help: Magnitude and angle counterclockwise from the + x direction

  1. Jan 28, 2012 #1
    1. The problem statement, all variables and given/known data
    Express your answer in part (a) in terms of magnitude and angle counterclockwise from the + x direction.
    Vector = -25.3i-1.2j


    2. Relevant equations
    arctan(ady/adx)


    3. The attempt at a solution
    Arctan(-1.2/25.3)=2.72
    This is wrong... but I have no idea how to fix it.
     
  2. jcsd
  3. Jan 28, 2012 #2
    Re: Vectors

    Since tan is a trig function that repeats every 90deg, some consideration must be put into the signs of x and y. Since x and y are both negative, 180deg must be added to the value calculated to obtain the correct value. Likewise, if y is negative and x is positive, 270deg must be added. If x is negative and y is positive, 90deg must be added. This is shown when looking at a plot of the tan function. To confirm this answer (182.72), plug it into tan and see if it gives you your y/x ratio.
     
  4. Jan 28, 2012 #3
    Re: Vectors

    Thank you very much that worked.
     
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