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How can I have a negative angle?

  1. Aug 9, 2008 #1
    1. The problem statement, all variables and given/known data

    Find the vector with the components: Ax=3.2 Ay= -5.15

    2. The attempt at a solution

    -5.15^2 + 3.2^2= 36.76
    sq root of 36.76= 6.06
    So, the magnitude is 6.06. Now for the direction....

    Tan theta=-5.15/3.2
    ArcTan(-1.6)= -57.99 degrees

    How can I have a negative angle?

    Thanks so much!
     
  2. jcsd
  3. Aug 9, 2008 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Re: Vectors

    ` What does the angle mean? If you were to actually draw that vector on an xy-coordinate system, you would draw it making that angle with the "positive x-axis"-to the right- measuring the angle "counter-clockwise" of course.. A negative angle would mean measuring clockwise- down rather than up. If you look at the y components, you will see that the reason the angle is negative is because the y component is negative- the vector points downward.
     
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