Results 1 to 3 of 3

Math Help - standard form of circles

  1. #1
    Newbie
    Joined
    Apr 2008
    Posts
    10

    standard form of circles

    my problem says find the center & radius os a circle x^2+6x+y^2-4y+4=0

    whats the formula i sold my book and im reviewing for my finals

    help please
    Follow Math Help Forum on Facebook and Google+

  2. #2
    o_O
    o_O is offline
    Primero Espada
    o_O's Avatar
    Joined
    Mar 2008
    From
    Canada
    Posts
    1,407
    Equations of circles are in the form of: (x-a)^{2} + (y - b)^{2} = r^{2}
    where (a, b) represents your centre of the circle (note the negative signs) and r (not r^{2}) represents your radius.

    For forms such as your question, you complete the square in respect to each variable:
    {\color{blue}x^{2}+6x} + {\color{red}y^{2}-4y+4}=0
    {\color{blue}x^{2} + 6x} + {\color{magenta}\left(\frac{6}{2}\right)^{2}} + {\color{red} (y-2)^{2} } = {\color{magenta}\left(\frac{6}{2}\right)^{2}}
    {\color{blue} (x+9)^{2} } + {\color{red} (y-2)^{2} } = 9
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Mar 2008
    Posts
    128
    Quote Originally Posted by bharriga View Post

    whats the formula i sold my book and im reviewing for my finals

    help please
    bad move...hopefully you don't do this next time. Sell them after your finals!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: March 9th 2010, 08:33 PM
  2. Replies: 1
    Last Post: February 16th 2010, 07:21 AM
  3. Circles and Standard Form
    Posted in the Algebra Forum
    Replies: 5
    Last Post: April 16th 2009, 07:22 AM
  4. Standard form/Slope-intercept form
    Posted in the Algebra Forum
    Replies: 1
    Last Post: February 9th 2009, 08:04 PM
  5. Replies: 14
    Last Post: May 30th 2008, 06:10 AM

Search Tags


/mathhelpforum @mathhelpforum