1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor

    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
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook