Results 1 to 6 of 6

Math Help - Completing the square

  1. #1
    Junior Member
    Joined
    May 2009
    Posts
    28

    Completing the square

    solve the following quadratic equation , solution in the form a \pm b \sqrt{n}

    a) 2x^2 -3x -3 = 0
    b) 3x^2 -6x +1 = 0

    thanks

    ps : for a i got completely messed up.
    for b i got 1 \pm \frac{\sqrt{2}}{3} but the answer from the maths book was 1 \pm \sqrt{\frac{2}{3}}
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    Jul 2009
    Posts
    190
    Thanks
    3
    a)

    2x^2 -3x -3 = 0
    2(x^2 -\frac{3}{2}x) -3= 0
    2((x-\frac{3}{4})^2-(\frac{3}{4})^2) -3= 0
    2((x-\frac{3}{4})^2)-2(\frac{3}{4})^2 -3= 0
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Jul 2009
    Posts
    190
    Thanks
    3
    This is the procedure;

    ax^2+bx+c=0
    a(x^2+\frac{b}{a}x)+c=0
    a((x+\frac{b}{2a})^2-(\frac{b}{2a})^2)+c=0
    a((x+\frac{b}{2a})^2)-a(\frac{b}{2a})^2+c=0
    a((x+\frac{b}{2a})^2)=a(\frac{b}{2a})^2-c
    (x+\frac{b}{2a})^2=(\frac{b}{2a})^2-\frac{c}{a}
    and solving this equation for x you get the quadratic formula.
    Last edited by Krahl; December 21st 2009 at 09:50 AM.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    May 2009
    Posts
    28
    thanks for the help, but i found out that is more easy to just take about the coeffecient of x out as a common factor, complete the sqaure, then just multiply it back in
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Senior Member
    Joined
    Jul 2009
    From
    Melbourne
    Posts
    272
    Thanks
    4
    stuffed the question up...
    Last edited by jgv115; December 21st 2009 at 11:10 PM.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Senior Member
    Joined
    Jul 2009
    From
    Melbourne
    Posts
    272
    Thanks
    4
    2x^2 -3x -3 = 0

    Same thing. Take out 2 as a common factor then divide coefficient by 2 and square.

    x^2-\frac{3}{2}x - \frac{3}{2} = 0

    Coefficient divide by 2:

     \frac{3}{2} * \frac{1}{2} = \frac{3}{4}

    Square:

     (\frac{3}{4})^2 = \frac{9}{16}

    Now complete the square by dividing the coefficient by 2

     (x-\frac{3}{4})^2 - \frac{33}{16} =0

    Can you do it from here.

    Do you understand everything I'm doing?
    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