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: Cardoid area

  1. Feb 14, 2007 #1
    1. The problem statement, all variables and given/known data

    Find the area of the region that is inside the circle r = 6cos(theta) but outside the cardoid r = 2 + 2cos(theta)

    2. Relevant equations

    r = 6·cosθ
    r = 2 + 2·cosθ

    3. The attempt at a solution

    intersections of the two curves.

    6·cosθ = 2 + 2·cosθ → 4·cosθ = 2

    cosθ = 1/2 → θ = ±π/3

    Can someone finish the integral for me, i'm not good at integrals, this is as far as i can get. thanks for any help.

    A = 2 x (1/2) ∫ [(6·cosθ)² - (2 + 2·cosθ)²] dθ
     
  2. jcsd
  3. Feb 14, 2007 #2

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    You still need a picture. Use math software and ask it to draw both graphs in polar coordinates (they should be [itex] \left(\rho,\varphi\right) [/itex], not "r" and "theta") and just then you can set up a correct integral.
     
  4. Feb 15, 2007 #3
    heres what i got so far.. can u please help finish this problem.

    heres where i'm at: http://img109.imageshack.us/img109/4070/untitledxz9.jpg [Broken]
     
    Last edited by a moderator: May 2, 2017
  5. Feb 16, 2007 #4

    HallsofIvy

    User Avatar
    Science Advisor

    No, I will not do the integral for you. I will give you a hint: to integrate [itex]cos^2(\theta)[/itex], use the trig identity [itex]cos^2(\theta)= \frac{1}{2}(cos(2\theta)+ 1).
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook