Results 1 to 4 of 4

Math Help - Solve the equation

  1. #1
    Member
    Joined
    Mar 2010
    Posts
    144

    Solve the equation

    Solve the equation algebraically for all values of x.

    8x^3 + 4x^2 - 18x - 9 = 0
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Dec 2009
    Posts
    3,120
    Thanks
    1
    Quote Originally Posted by MATNTRNG View Post
    Solve the equation algebraically for all values of x.

    8x^3 + 4x^2 - 18x - 9 = 0
    Notice that this is

    (2x)^3+(2x)^2-9(2x)-9=0

    2x=-1 is a solution, so (2x+1) is a factor.

    (2x+1)\left(4x^2+bx-9) are the factors, so you only need find "b" and factor the quadratic.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    A riddle wrapped in an enigma
    masters's Avatar
    Joined
    Jan 2008
    From
    Big Stone Gap, Virginia
    Posts
    2,551
    Thanks
    12
    Awards
    1
    Quote Originally Posted by MATNTRNG View Post
    Solve the equation algebraically for all values of x.

    8x^3 + 4x^2 - 18x - 9 = 0


    Hi MATNTRNG,

    First, factor by grouping.

    8x^3+4x^2-18x-9=0

    (8x^3+4x^2)-(18x+9)=0

    4x^2(2x+1)-9(2x+1)=0

    (4x^2-9)(2x+1)=0

    I'll bet you can take it from here. Right?


    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,677
    Thanks
    1618
    Awards
    1
    Quote Originally Posted by MATNTRNG View Post
    Solve the equation algebraically for all values of x.

    8x^3 + 4x^2 - 18x - 9 = 0
    8x^3+4x^2-18x-9=4x^2(2x+1)-9(2x+1)
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Solve Differential equation for the original equation
    Posted in the Differential Equations Forum
    Replies: 5
    Last Post: February 21st 2011, 01:24 PM
  2. need to solve summation equation to solve sum(x2)
    Posted in the Statistics Forum
    Replies: 2
    Last Post: July 16th 2010, 10:29 PM
  3. how can i solve this equation for x
    Posted in the Calculus Forum
    Replies: 7
    Last Post: November 29th 2009, 01:43 PM
  4. Replies: 13
    Last Post: May 19th 2008, 08:56 AM
  5. solve equation
    Posted in the Algebra Forum
    Replies: 1
    Last Post: May 4th 2007, 12:06 AM

Search Tags


/mathhelpforum @mathhelpforum