Results 1 to 3 of 3

Math Help - circle

  1. #1
    Newbie
    Joined
    Jul 2007
    Posts
    2

    circle

    A coin is unique in that the outer edge is gold while the inside is silver. Assuming both sides of the coin are identical, and a line tangent to the inner circle is 23 mm from edge to edge of the coin, and excluding the edge of the coin in the calculation, what is the surface area of gold on the coin, in square millimetres? Please round up to the nearest square millimetre.

    I am really not good at this, can someone point me in the right direction please?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor red_dog's Avatar
    Joined
    Jun 2007
    From
    Medgidia, Romania
    Posts
    1,252
    Thanks
    5
    If R is the radius of the coin and r is the radius of the silver circle, the gold area is \pi R^2-\pi r^2=\pi (R^2-r^2).
    We have R^2-r^2=\left(\frac{23}{2}\right)^2.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jul 2007
    Posts
    2
    Thank you!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Circle, tangent line, and a point not on the circle
    Posted in the Pre-Calculus Forum
    Replies: 5
    Last Post: March 31st 2011, 01:40 PM
  2. Replies: 6
    Last Post: July 8th 2010, 05:39 PM
  3. Replies: 7
    Last Post: March 15th 2010, 04:10 PM
  4. Replies: 2
    Last Post: February 6th 2010, 08:31 AM
  5. Replies: 0
    Last Post: October 12th 2008, 04:31 PM

Search Tags


/mathhelpforum @mathhelpforum