Results 1 to 8 of 8

Math Help - Completing The Square

  1. #1
    Newbie
    Joined
    Feb 2010
    Posts
    4

    Smile Completing The Square

    Do people know how to complete the square

    For Example:
    3x2 - 15x + 18 = 0

    (Note: 3x2 means 3x squared)
    Last edited by Chris L T521; February 16th 2010 at 07:27 AM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Feb 2010
    Posts
    4
    pull out the common factor of 3, which leaves you:

    3(x^2 - 5x + 6) = 0 ----> 3(x-3)(x-2) = 0

    x= 3 and x=2
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2010
    Posts
    4
    OMG!! Mathless i absolutely love u!!!!
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,569
    Thanks
    1428
    Quote Originally Posted by liveboon View Post
    Do people know how to complete the square

    For Example:
    3x2 - 15x + 18 = 0

    (Note: 3x2 means 3x squared)
    3x^2 - 15x + 18 = 0

    3(x^2 - 5x + 6) = 0

    3\left[x^2 - 5x + \left(-\frac{5}{2}\right)^2 - \left(-\frac{5}{2}\right)^2 + 6\right] = 0

    3\left[\left(x - \frac{5}{2}\right)^2 - \frac{25}{4} + \frac{24}{4}\right] = 0

    3\left[\left(x - \frac{5}{2}\right)^2 - \frac{1}{4}\right] = 0

    3\left(x - \frac{5}{2}\right)^2 - \frac{3}{4} = 0.
    Last edited by mr fantastic; February 17th 2010 at 01:07 AM.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,569
    Thanks
    1428
    P.S. Someone please lock this thread - there's no need for outbursts like that!
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Banned
    Joined
    Oct 2009
    Posts
    4,261
    Thanks
    2
    Quote Originally Posted by liveboon View Post
    Do people know how to complete the square

    For Example:
    3x2 - 15x + 18 = 0

    (Note: 3x2 means 3x squared)

    In general, ax^2+bx+c=a\left(x+\frac{b}{2a}\right)^2 +c-\frac{b^2}{4a} , and perhaps you can recognize the term c-\frac{b^2}{4a}=-\frac{\Delta}{4a}\,,\,\,\Delta= the quadratic's discriminant.

    So yes, I think some people know how to complete the square.

    Tonio
    Last edited by mr fantastic; February 17th 2010 at 01:08 AM.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Banned
    Joined
    Oct 2009
    Posts
    4,261
    Thanks
    2
    Quote Originally Posted by Mathless View Post
    pull out the common factor of 3, which leaves you:

    3(x^2 - 5x + 6) = 0 ----> 3(x-3)(x-2) = 0

    x= 3 and x=2

    I'm afraid this is not what the OP asked for, though she/he seems to be unaware of it. What you did here is to factor the quadratic, which is very useful to calculate its roots, for example, but it's not completing the square.

    Tonio
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Rhymes with Orange Chris L T521's Avatar
    Joined
    May 2008
    From
    Chicago, IL
    Posts
    2,844
    Thanks
    3
    I've seen enough happen here in this thread. Now that the question has been answer, there is no need to continue posting here.

    Thread closed.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Completing the square.
    Posted in the Algebra Forum
    Replies: 4
    Last Post: September 23rd 2010, 08:51 AM
  2. completing the square
    Posted in the Algebra Forum
    Replies: 10
    Last Post: September 16th 2009, 10:58 AM
  3. completing the square?
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: August 13th 2009, 10:17 AM
  4. Completing The Square
    Posted in the Algebra Forum
    Replies: 2
    Last Post: September 4th 2007, 05:18 AM
  5. Completing the Square
    Posted in the Algebra Forum
    Replies: 7
    Last Post: August 31st 2007, 10:36 PM

Search Tags


/mathhelpforum @mathhelpforum