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Homework Help: Vector Components and Finding the Angle

  1. Sep 18, 2006 #1
    Let the angle theta be the angle that the vector A makes with the +x-axis, measured counterclockwise from that axis. Find the angle theta for a vector that has the following components:

    A_x = -4.50m
    A_y = -3.30m

    Using the calculator, I got arctan(-3.30m/-4.50 m) = 36.25 degrees.

    However, this answer is wrong. I know the angle is supposed to be counterclockwise from +x-axis, but I thought the signs canceled out. What is the correct way of determining the angle?

    Last edited: Sep 19, 2006
  2. jcsd
  3. Sep 18, 2006 #2
    your answer is right, but your frame of reference is off.

    where is an angle theta equal to 0 at? think about how the problem stated the increase in theta.

    did you draw a picture?
  4. Sep 19, 2006 #3
    Well, I drew vector A in quadrant 3 and subtracted the angle from 270 (270 - 36.25 = 234), but that answer is wrong.
    Last edited: Sep 19, 2006
  5. Sep 19, 2006 #4


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    You should be measuring anti clockwise, add 180o to your original answer.
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