Results 1 to 2 of 2

Math Help - What is the area between the two circles?

  1. #1
    Senior Member
    Joined
    Apr 2006
    Posts
    290

    What is the area between the two circles?

    If the length of AB is 20cm.

    What is the area between the two circles?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by Natasha1
    If the length of AB is 20cm.

    What is the area between the two circles?
    Label the centre of the circle O, the midpoint of AB M
    the radius of the smaller circle r_1 and the radius of the outer circle r_2.

    Then triangle OMB is a right triangle with hypotenuse r_2
    and the other sides r_1, and 10. Therefore by Pythagoras:

    <br />
r_2^2=10^2+r_1^2<br />
,

    or:

    <br />
r_2^2-r_1^2=100<br />

    The area of the annulus is:

    <br />
\pi r_2^2 - \pi r_1^2=\pi (r_2^2-r_1^2)=\pi.100 <br />

    RonL
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Area of overlap of two circles.
    Posted in the Geometry Forum
    Replies: 2
    Last Post: November 27th 2011, 05:20 AM
  2. Circles area proving
    Posted in the Geometry Forum
    Replies: 1
    Last Post: June 11th 2010, 02:17 AM
  3. Area between two circles
    Posted in the Calculus Forum
    Replies: 5
    Last Post: April 12th 2010, 09:51 PM
  4. Area between Circles
    Posted in the Geometry Forum
    Replies: 4
    Last Post: November 2nd 2009, 01:00 PM
  5. Replies: 2
    Last Post: October 6th 2009, 09:04 AM

Search Tags


/mathhelpforum @mathhelpforum