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Polar Coordinates and Conics, need help bad

  1. Apr 18, 2008 #1
    Were on the conic section. I need help how to choose the right interval to evaluate the arc lengh. x=5cost-cos5t and y=5sint-sin5t . I dont get how to choose the inverval to evaluate this, can someone pleasse tell me how. I just dont grasp this.
  2. jcsd
  3. Apr 19, 2008 #2
    Does this help?

    [tex]= \int_{a}^{b} \sqrt { [x'(t)]^2 + [y'(t)]^2 }\, dt.[/tex]

    5 cos(t) - cos(5t) and 5 sin(t)- sin(5t) will no doubt fall within an area between [itex]x\pi \theta[/itex] and [itex]x\pi\theta[/itex] do you know how to work that out? Or how to work out appropriate ranges for cos and sin?

    Personally I'd chose something like between 0 and [itex]\pi[/itex]... or 0 and [itex]2\pi[/itex]
    Last edited: Apr 19, 2008
  4. Apr 19, 2008 #3


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    Those parametric equations do NOT give a conic section.

    You can, however, cover the figure by letting t go from 0 to [itex]2\pi[/itex]
  5. Apr 19, 2008 #4
    how do i mathematically find the right interval to evaulate it ?
  6. Apr 20, 2008 #5
    Which range will your shape fall in?

    It's between the range of 0 and 360 degrees (or a full circle) right? In that case what is the range/interval in degrees to radians? Couldn't be 0 to 2[itex]\pi[/itex] could it?


    Last edited: Apr 20, 2008
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