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Homework Help: Polar coordinates math

  1. Nov 9, 2013 #1
    1. The problem statement, all variables and given/known data

    Convert (1,-2) to polar coordinates find one representation with r >0 and one with r <0. Also 0<= theta <= 2 PI

    2. Relevant equations

    I used tantheta = y /x , and x^2 +y^2 = r^2

    3. The attempt at a solution

    I got (sqrt(5) , arctan(-2)) , (-sqrt(5) , arctan(-2) + pi )
    Is this OK?
  2. jcsd
  3. Nov 9, 2013 #2


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    Staff Emeritus
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    Does arctan(-2) satisfy 0 <= theta <= 2 pi?
  4. Nov 9, 2013 #3
    I think so it is -63.43 degrees in my calculator and I forget how arctan comes back in the calculator but if I add 180 to that it is still only 116. I forget where is comes back to the domain on the calculator I mean.
  5. Nov 9, 2013 #4


    Staff: Mentor

    But -63.43° is not in the interval [0°, 360°]. That was essentially what SteamKing was objecting to.
  6. Nov 9, 2013 #5
    OH opps. OK so add 360 to it. Then I'm good right?
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