Results 1 to 2 of 2

Math Help - Standard form!

  1. #1
    Newbie
    Joined
    Oct 2006
    Posts
    4

    Arrow Standard form!

    okay so the question is as follows!
    use X^2+ y^2-6x+8y+ 9= 0
    write the equation in standard form!

    so here is waht I have done!

    X^2+ y^2 -6x +8y+ 9= 0

    X^2+ y^2 -6x +8y=-9

    now I have to remove the coefiicent from X^2 and y^2
    1(X^2-6x) +1( y^2 +8y) =-9

    Now I have to complete the squares but I get lost from here I am unsure how to do it! thanks!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,966
    Thanks
    350
    Awards
    1
    Quote Originally Posted by cutie4ever View Post
    okay so the question is as follows!
    use X^2+ y^2-6x+8y+ 9= 0
    write the equation in standard form!

    so here is waht I have done!

    X^2+ y^2 -6x +8y+ 9= 0

    X^2+ y^2 -6x +8y=-9

    now I have to remove the coefiicent from X^2 and y^2
    1(X^2-6x) +1( y^2 +8y) =-9

    Now I have to complete the squares but I get lost from here I am unsure how to do it! thanks!
    If you have x^2 + 2ax then you add and subtract a^2:

    x^2 - 6x:
    2a = -6, so a = -3 so a^2 = 9:

    (x^2-6x + 9 - 9) +(y^2 +8y) =-9

    (x^2 - 6x + 9) - 9 + (y^2 +8y) =-9

    (x - 3)^2 + (y^2 +8y) = 0

    Similarly:
    (x - 3)^2 + (y^2 + 8y + 16 - 16) = 0

    (x - 3)^2 + (y^2 + 8y + 16) - 16 = 0

    (x - 3)^2 + (y + 4)^2 = 16

    (x - 3)^2 + (y + 4)^2 = 4^2

    So the equation is for a circle of radius 4 with center at (3, -4).

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 3
    Last Post: February 3rd 2011, 06:41 PM
  2. Replies: 2
    Last Post: March 9th 2010, 08:33 PM
  3. Replies: 1
    Last Post: February 16th 2010, 07:21 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