Results 1 to 8 of 8
Like Tree1Thanks
  • 1 Post By HallsofIvy

Math Help - Factoring help, again...

  1. #1
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Factoring help, again...

    -(x-2)(x^2+2x+5)
    -(x^3+2x^2+5x-2x^2+4x-10)
    -(x^3+x-10)
    -x^3-x+10

    How do you factor this? I tried adding in a 0x^2 and grouping, but that didn't work out. The other group can't factor out to x-0...
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,619
    Thanks
    592

    Re: Factoring help, again...

    Hey Nervous.

    Try factoring the quadratic by getting the roots through the quadratic formula.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Re: Factoring help, again...

    I thought quadratics were only second degree polynomials...?


    EDIT: Ohhhhh I get it, you meant the first trinomial... OK...
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,579
    Thanks
    1418

    Re: Factoring help, again...

    Why in the world would you first multiply and then factor? You start with -(x- 2)(x^2+ 2x+ 5) so obviously, one factor is x- 2. In order to factor x^2+ 2x+ 5 into factors with integer coefficients, I would note that 5 factors only as 1(5) but neither 5-1 nor 5+ 1 is equal to 2 so we can't factor with integer coefficients. Not every quadratic can be factored with integer (or even real) coefficients.

    So instead, complete the square! x^2+ 2x+ 1= (x+ 1)^2 so that x^2+ 2x+ 5= x^2+ 2x+ 1+ 4= (x+1)^2+ 4= (x+1)^2- (-4)= (x+ 1)^2- (2i)^2. Now use the identity a^2- b^2= (a- b)(a+ b).
    Thanks from MarkFL
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Re: Factoring help, again...

    That's a beautiful idea... God, I still have so much to learn...
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Re: Factoring help, again...

    Another one:
    2x^3+11x^2-12x-36

    I tried grouping, I tried factoring out an x and using quadratic formula on x^+11x-12 I don't know how to do this one.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Re: Factoring help, again...

    Edit
    Quote Originally Posted by nervous View Post
    another one:
    2x^3+11x^2-12x-36

    i tried grouping, i tried factoring out an x and using quadratic formula on x^2+11x-12 i don't know how to do this one.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,901
    Thanks
    329
    Awards
    1

    Re: Factoring help, again...

    Have you tried the "Rational Root Test?"

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. factoring ?
    Posted in the Algebra Forum
    Replies: 2
    Last Post: March 25th 2010, 06:38 PM
  2. Factoring
    Posted in the Algebra Forum
    Replies: 4
    Last Post: September 15th 2009, 04:44 PM
  3. Replies: 2
    Last Post: August 22nd 2009, 10:57 AM
  4. factoring help
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 30th 2008, 08:46 AM
  5. Replies: 3
    Last Post: November 5th 2006, 11:02 PM

Search Tags


/mathhelpforum @mathhelpforum