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Parametric equation to cartesian

  1. Oct 5, 2014 #1
    1. The problem statement, all variables and given/known data
    I have this equation and i need to find the cartesian equation, so i apreciate your help

    2. Relevant equations
    X=cost ' y=2sin2t

    3. The attempt at a solution
    I am usign this

    Sin2t=2costsint
    So x+y/2=cost+2costsint
    But i dont know what to do after,
    I also try to solve that this way
    Y/2=sin2t
    Y/2=2costsint then sint=y/(4cost)
    Y/2=2((x)y/4x)
    When i isolate y i get y/y=3x-2
     
  2. jcsd
  3. Oct 6, 2014 #2

    Mark44

    Staff: Mentor

    So y = 4sin(t)cos(t). What is y/x?

    Ideally, you want to get something that involves sin2(t) + cos2(t), which equals 1, and eliminates the parameter t.
     
  4. Oct 6, 2014 #3
    Thanks for the help i juts figure out how to get rid of that parameter 1-cos alll div by 2
     
  5. Oct 6, 2014 #4

    Mark44

    Staff: Mentor

    I doubt that will work.
     
  6. Oct 6, 2014 #5
    y=4xsint==>y^2=16x^2(1(cost)^2)=y^2=16x^2(1-x^2)
     
  7. Oct 6, 2014 #6
    Forget about div for 2
     
  8. Oct 6, 2014 #7

    Mark44

    Staff: Mentor

    With one correction, that works. Where you have y2 = 16x2(1(cost)^2), it should be y2 = 16x2(1 - cos2(t)). Otherwise, what you ended with is the same as I got.
     
  9. Oct 6, 2014 #8
    Thanks thats it Sorry pal i have anoter problem i am doing x=sect y=tant
    So what i need to do use the 1+tan^2=sec^2
    Or use the sin/cos=tan and 1/cos = sec? I can get the solution
     
  10. Oct 6, 2014 #9

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Using ##1 + \tan^2\theta = \sec^2\theta## is the obvious choice. But you should post new questions in new threads if you don't want to have your hand slapped by a moderator.
     
  11. Oct 6, 2014 #10

    Mark44

    Staff: Mentor

    This is a new problem, so please start a new thread.
     
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