1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    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!

Homework Help: Polar coordinates from rectangle

  1. Feb 7, 2006 #1
    Heres where Im struggling, I cant seem to change equations from rectangular to polar and vice versa

    an example


    heres what I got when I tried
    r=2a cos theta
    and thats a graph of a rose curve, I think, Im about 10% sure on that answer

    heres an example of one I have no clue on


    heres what im thinkin on this one

    the x^2+y^2 can = r^2 and the arctan (y/x) can = theta
    so you would have (r^2)(theta^2)=a^2

    I dont know, I just cant get this
  2. jcsd
  3. Feb 8, 2006 #2


    User Avatar
    Science Advisor
    Homework Helper

    What, exactly, are you having doubts about? It looks fine to me.
  4. Feb 8, 2006 #3


    User Avatar
    Science Advisor

    Okay, obviously [itex]x^2+ y^2= r^2[/itex] and [itex]2ax= 2ar cos(\theta)[/itex] so the is [itex]r^2- 2ar cos(\theta)= 0[/itex] which you can write as [itex]r^2= 2ar cos(\theta)[/itex] and, as long as r is not 0, divide by r to get [itex]r= 2a cos(\theta)[/itex] as you have.

    Again [itex]r^2= x^2+ y^2[/itex] and, essentially by definition, [itex]arctan(y/x)= \theta[/itex] so this is simply [itex]r2\theta^2= a^2[/itex] as you have.
    Assuming everything is positive, you can reduce that to [itex]r\theta= a[/itex].
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook