Results 1 to 5 of 5

Math Help - ring question..

  1. #1
    MHF Contributor
    Joined
    Nov 2008
    Posts
    1,401

    ring question..

    basically what i need is to find the area of the ring
    the with is dr and the radius is r
    so dA=pi*(r+dr)^2 - pi*(r)^2
    so why the dA is that simple expression??

    http://www.freeimagehosting.net/imag...cce537487f.gif
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jan 2009
    Posts
    591
    Quote Originally Posted by transgalactic View Post
    basically what i need is to find the area of the ring
    the width is dr and the radius is r
    so dA=pi*(r+dr)^2 - pi*(r)^2
    so why the dA in that simple expression??
    Your equation above is correct for the annulus.
    However, in the image:  \sigma d A does not refer to the annulus.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Joined
    Nov 2008
    Posts
    1,401
    its a part of anulus
    whats the logic of calculating area in double integral
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    May 2007
    Posts
    237
    Quote Originally Posted by aidan View Post
    Your equation above is correct for the annulus.
    However, in the image:  \sigma d A does not refer to the annulus.
    2\pi{rdr} is an approximate value. The (dr)^2 is omitted.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    Joined
    Nov 2008
    Posts
    1,401
    this is the simple way
    i want to know how to calculate that with double integral
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Question about Ring Homomorphism
    Posted in the Advanced Algebra Forum
    Replies: 7
    Last Post: April 19th 2011, 03:19 AM
  2. Ring Theory Question
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: March 12th 2011, 07:19 PM
  3. Ring Isomorphism Question
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: October 12th 2009, 07:35 PM
  4. Finite ring question.
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: March 15th 2009, 08:26 PM
  5. Question about Ring
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: June 17th 2008, 08:12 PM

Search Tags


/mathhelpforum @mathhelpforum