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What is the angle between

  1. Sep 1, 2008 #1
    1. The problem statement, all variables and given/known data
    The x component of a certain vector is -45.0 units and the y component is +42.0 units.

    a) What is the magnitude of the vector?
    61.56 units <----- I got this right

    b) What is the angle between the direction of the vector and the positive direction of x? Use the convention that positive angles are measured counterclockwise from the +x axis and negative angles are measured clockwise from the +x axis.

    2. Relevant equations

    3. The attempt at a solution

    For part b) I put -43.02 for the angle but that was wrong. I'm guessing I have to subtract this angle from 180 which is 136.9. Is that the correct answer for b? Any help would be appreciated. Thanks.
  2. jcsd
  3. Sep 1, 2008 #2


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    Homework Helper

    Use a little bit of geometry. Look at the angle that the vector forms with the positive Y-axis. Then you can add that to 90 degrees. (Which gives you your 136.9 degrees btw.)
    Last edited: Sep 1, 2008
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