Results 1 to 2 of 2

Thread: Argh

  1. #1
    Junior Member
    Oct 2005


    Every week I always have to spend hours trying to understand what we did in the lesson, here's the latest thing that's making me feel worthless.

    Solve the Quadratic Equation by completing the square leaving the answer in surd form

    10 = 3x - x^2

    rearranged i know it's

    x^2 - 3 = 10 (i think)

    Please help! (This is the hardest one, so if I can do this the others shouldn't present a problem)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Oct 2005
    When you are asked to complete a sqaure you must end up with something like " (X + something) + something else = 0 "

    If for example you have (X + A) this gives X+ 2A.X + A
    You should be able to multiply out brackets

    The point of completing the square is to do that in reverse.
    With your equation you have:
    X - 3X + 10 = 0

    With my example you will notice that I had 'A' inside the bracket, and 2A as the coefficent for X. Conversely you have -3X, so inside the bracket you need -1.5.


    However this is not the correct answer. If you were to multiply out that bracket you would end up with a + 2.25 (-1.5x-1.5), instead of the +10 that you want. The solution to this is just put another +7.75 on the end of that.

    Hence after completing the square:

    X - 3X + 10 = 0 is the same as (X - 1.5) + 7.75 = 0

    I believe this is correct.

    edit : Not quite sure what it means by surd form. I thought that was to do with square roots....
    Last edited by TheBrain; Oct 6th 2005 at 08:20 AM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Argh! Not story problems!!!
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: Mar 7th 2010, 11:20 AM
  2. Lagrange Argh...
    Posted in the Calculus Forum
    Replies: 5
    Last Post: Oct 17th 2009, 07:28 PM
  3. Argh!! Really stuck!! Please help
    Posted in the Differential Equations Forum
    Replies: 5
    Last Post: Apr 10th 2009, 04:27 AM
  4. Old math tests... Argh!
    Posted in the Statistics Forum
    Replies: 2
    Last Post: May 28th 2007, 09:25 AM
  5. Argh. lost ! Volume
    Posted in the Geometry Forum
    Replies: 3
    Last Post: Nov 10th 2006, 05:48 AM

Search Tags

/mathhelpforum @mathhelpforum