Results 1 to 5 of 5
Like Tree3Thanks
  • 1 Post By chiro
  • 1 Post By Prove It
  • 1 Post By Soroban

Math Help - Finding x when x has different indices. How do I simplify, please?

  1. #1
    Newbie
    Joined
    Jan 2013
    From
    UK
    Posts
    2

    Finding x when x has different indices. How do I simplify, please?

    12x^6 + 7x^4 = 9315

    Forgive my inadequacies, but could somebody show the steps I need to make x the subject?
    I don't know how to do this when x doesn't have the same power index.
    Any help appreciated. Thanks.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,649
    Thanks
    601

    Re: Finding x when x has different indices. How do I simplify, please?

    Hey TheDunce.

    You will have to transform this into a cubic using the transformation u = x^2 to get 12u^3 + 7u^2 - 9315 = 0 and then use the cubic formula to solve for u first and then x using the relation between x and u.

    Cubic function - Wikipedia, the free encyclopedia
    Thanks from TheDunce
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,548
    Thanks
    1418

    Re: Finding x when x has different indices. How do I simplify, please?

    Here's some information about the Cubic Formula.
    Attached Files Attached Files
    Thanks from TheDunce
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,738
    Thanks
    643

    Re: Finding x when x has different indices. How do I simplify, please?

    Hello, TheDunce!

    \text{Solve: }\:12x^6 + 7x^4 \:=\: 9315

    I don't know how to do this when x doesn't have the same power index. ??
    Does this mean that you have never ever solved a quadratic equation?
    Then who assigned you a sixth-degree equaton?


    We have: . 12x^6 + 7x^4 - 9315 \:=\:0

    We find that x = \pm3 are roots of the equation

    . . and that: . 12x^6 + 7x^4 - 9315 \;=\;(x^2-9)(12x^4 + 115x^2 + 1035)

    The quartic has no real roots.

    Therefore, the only real roots are: . x \:=\:+3,\,-3
    Thanks from TheDunce
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jan 2013
    From
    UK
    Posts
    2

    Re: Finding x when x has different indices. How do I simplify, please?

    Thanks for the quick replies. I will study this. I'm trying to learn from a textbook and didn't know where to start on this one.
    Soroban: I've solved some quadratic equations and used the quadratic formula so I guess the comment didn't make sense. Thanks for the help.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 7
    Last Post: November 10th 2011, 11:57 AM
  2. Simplify involving indices
    Posted in the Algebra Forum
    Replies: 4
    Last Post: October 3rd 2009, 09:15 AM
  3. need help with indices simplify
    Posted in the Algebra Forum
    Replies: 2
    Last Post: August 12th 2009, 12:06 AM
  4. Simplify the following indices
    Posted in the Algebra Forum
    Replies: 38
    Last Post: February 1st 2009, 01:43 AM
  5. Replies: 3
    Last Post: December 14th 2008, 05:54 AM

Search Tags


/mathhelpforum @mathhelpforum