Results 1 to 3 of 3

Math Help - I don't know where to stop...!!!

  1. #1
    Member
    Joined
    Dec 2007
    Posts
    96

    Thumbs up I don't know where to stop...!!!

    Please, see the attached document, for I was unable to write it using Latex.
    Attached Files Attached Files
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Alienis Back View Post
    Please, see the attached document, for I was unable to write it using Latex.
    The question is:

    How to solve 9x^2 + 6x - 8 = 0.

    The approach you're trying to use is completing the square. You've done well to get to here:

    9\left[ \left(x + \frac{1}{3}\right)^2 - 1 \right] = 0.

    Unfortunately you then proceed to undo all this, effectively going in a circle and arriving back to 9x^2 + 6x - 8 = 0.

    Here is what you must do. Divide both sides of 9\left[ \left(x + \frac{1}{3}\right)^2 - 1 \right] = 0 by 9:

    \left(x + \frac{1}{3}\right)^2 - 1 = 0

    \Rightarrow \left(x + \frac{1}{3}\right)^2 - 1^2 = 0

    which is clearly a difference of two squares.

    From your previous posts I know that you (should) know how to factorise this and hence get the solution.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member great_math's Avatar
    Joined
    Oct 2008
    Posts
    132
    How to solve .

    A better approach...

    9x^2+6x-8=0
    Multiply a 4 to LHS and RHS

    It becomes 36x^2+24x-32=0

    \implies(6x)^2+2\cdot 6x\cdot 2+4-36=0

    \implies(6x+2)^2-6^2=0

    \implies (6x-4)(6x+8)=0

    \implies x=\left\{\frac 2{3},\frac {-4}{3}\right\}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. propability, train stop
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: December 6th 2011, 04:09 AM
  2. How to stop execution of mat-lab program
    Posted in the Math Software Forum
    Replies: 1
    Last Post: May 26th 2010, 12:36 PM
  3. Replies: 1
    Last Post: December 14th 2009, 06:59 PM
  4. Probability that no 2 people get off at some stop
    Posted in the Statistics Forum
    Replies: 3
    Last Post: October 29th 2009, 03:16 PM
  5. stop that bus!
    Posted in the Advanced Statistics Forum
    Replies: 17
    Last Post: July 13th 2008, 12:34 AM

Search Tags


/mathhelpforum @mathhelpforum