Results 1 to 2 of 2

Math Help - Polar Equation to Coordinate

  1. #1
    Newbie
    Joined
    Jan 2010
    Posts
    11

    Polar Equation to Coordinate

    Hello. I don't have the slightest idea of how to change this equation:
    r = 3cos(2q) (q being an angle, call it theta, or whatever) to coordinate form.

    i know that x=r cosq and y=r sinq but how i can use this to convert to the coordinate form?

    thank you. if you can please show me a step by step to undersand it well.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,735
    Thanks
    642
    Hello, guidol92!

    You need a trig identity like: . \cos2\theta \:=\:\cos^2\theta - \sin^2\theta


    Write in rectangular coordinates: .  <br />
r \:=\:3\cos(2\theta)
    Multiply by r^2\!:\;\;\;r^3 \:=\:3r^2\cos2\theta \;=\;3r^2(\cos^2\theta-\sin^2\theta ) \;=\;3\bigg[r^2\cos^2\theta - r^2\sin^2\theta\bigg]

    . . . . . . . . . . r^3 \;=\;3\bigg[(r\cos\theta)^2 - (r\sin\theta)^2\bigg]

    . . . . (\sqrt{x^2+y^2})^3 \;=\;3(x^2 - y^2)<br />


    . . . . . . (x^2+y^2)^3 \;=\;9(x^2-y^2)^2

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: August 10th 2010, 11:15 PM
  2. polar coordinate equation
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: July 19th 2010, 12:28 AM
  3. Polar coordinate
    Posted in the Calculus Forum
    Replies: 0
    Last Post: April 16th 2010, 01:49 AM
  4. polar coordinate
    Posted in the Calculus Forum
    Replies: 4
    Last Post: July 24th 2007, 08:13 PM
  5. Polar Coordinate 03
    Posted in the Calculus Forum
    Replies: 3
    Last Post: July 21st 2007, 06:00 PM

Search Tags


/mathhelpforum @mathhelpforum