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Homework Help: Angle of vector

  1. Sep 5, 2011 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    So, given these two components of the vector A, to find the angle the vector makes with the X axis I simply did the following:


    So theta is -71.1 with significant figures.

    and that's not the expected answer either?
    What am I doing wrong?

    Do they really want the angle "measured counterclockwise from that axis" meaning:
    360-71.1 ?
    Last edited: Sep 5, 2011
  2. jcsd
  3. Sep 5, 2011 #2


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    Homework Helper
    Gold Member

    -71.1 looks right, so does 360-71.1. You have 4 shots left, why not give it a try?
  4. Sep 5, 2011 #3
    I think each "shot" takes off some points. Because the instructions says that it wants the angle counterclockwise from the +x axis, (which I assume is the positive side of the x axis) then I am thinking that the latter answer is correct.

    This is silly, considering all the talk about "bowtie" angles and whatnot by my actual professor in class.
  5. Sep 5, 2011 #4


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    Gold Member

    If the automated answer checking machine cannot deal with negative angles, that is a limitation of the machine, not you. If, as a result of this machine limitation, you have wasted a shot by entering a perfectly valid -71.1 degrees (with respect to positive angles being measured in the CCW direction from the +x axis) then you should insist that your professor return those couple of points only if you are between grades and think that a couple of points will matter. Otherwise, don't worry about it and fire away with the positive angle answer.

    P.S. How do you know the machine is looking for degrees, not radians? What are the ground rules for submitting angle results?
  6. Sep 5, 2011 #5
    There is a little degree symbol next to the answer field.

    I'm down to my last shot at this question, this is frustrating because I know that every single one of my answers were correct.
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