Results 1 to 3 of 3

Math Help - Quadratic Formula

  1. #1
    Newbie
    Joined
    Sep 2007
    Posts
    12

    Quadratic Formula

    Im stuck on one of my questions in my book, i've got all the others right but this one has really stumped me. Im doing the same steps as the other questions so im pretty sure im missing something. I think im doin something wrong when im expanding each side of the equation and then simplifying.

    Use the quadratic formula to solve the equation, rounding you answer to two decimal places.

    2(x^2-1) = 15(x+3)
    2x^2-2 = 15x+45
    2x^2-15x-47=0
    a=2, b=-15, c=-47

    x= (--15) +- (sqrt)(-15^2 -4(2)(-47)))/4
    x= (15 +- (sqrt)151)/4
    x= (15+(sqrt)151)/4  or  (15-(sqrt)151)/4

    Does my attempt at writing the question make sense? Thanks
    x=6.82  or  x=0.68
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member DivideBy0's Avatar
    Joined
    Mar 2007
    From
    Melbourne, Australia
    Posts
    432
    The discriminant is incorrect, the rest of the problem is correct.

    2x^2-15x-47=0

    x=\frac{-(-15)\pm \sqrt{(-15)^2-4(2)(-47)}}{2(2)}

    =\frac{15 \pm \sqrt{225+376}}{4}

    =\frac{15 \pm \sqrt{601}}{4}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,211
    Thanks
    419
    Awards
    1
    Quote Originally Posted by Local_lunatic View Post
    x=6.82  or  x=0.68
    Unless you have a specific reason, you should leave your answer in exact form, not in decimals.

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Quadratic Formula.
    Posted in the Algebra Forum
    Replies: 3
    Last Post: March 23rd 2011, 12:19 PM
  2. quadratic formula
    Posted in the Algebra Forum
    Replies: 1
    Last Post: February 25th 2010, 12:08 PM
  3. quadratic formula
    Posted in the Algebra Forum
    Replies: 3
    Last Post: September 2nd 2009, 03:57 PM
  4. quadratic formula
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 14th 2008, 11:47 PM
  5. Quadratic Formula
    Posted in the Algebra Forum
    Replies: 2
    Last Post: April 8th 2008, 05:05 PM

Search Tags


/mathhelpforum @mathhelpforum