Results 1 to 6 of 6

Math Help - raftional expression?

  1. #1
    Junior Member
    Joined
    Apr 2012
    From
    bowie md
    Posts
    34

    raftional expression?

    x2-x-12 . 3+x
    x2-9 4-x

    ans (x-4)(3+X)
    (X-3)(4-X)

    THERE IN THE BOOK IS (3+X)
    (X-3)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Reckoner's Avatar
    Joined
    May 2008
    From
    Baltimore, MD (USA)
    Posts
    1,024
    Thanks
    75
    Awards
    1

    Re: raftional expression?

    Quote Originally Posted by zbest1966 View Post
    THERE IN THE BOOK IS (3+X)
    (X-3)
    Note that (4-x) = -(x-4).

    In general, (a-b)=-(b-a).

    Edit: I didn't look too closely at the book's answer, but the other two posters are correct when they say that it is wrong.
    Last edited by Reckoner; June 10th 2012 at 07:03 AM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,560
    Thanks
    1425

    Re: raftional expression?

    Quote Originally Posted by zbest1966 View Post
    x2-x-12 . 3+x
    x2-9 4-x

    ans (x-4)(3+X)
    (X-3)(4-X)

    THERE IN THE BOOK IS (3+X)
    (X-3)
    \displaystyle \begin{align*} \frac{x^2 - x - 12}{x^2 - 9} \cdot \frac{3 + x}{4 - x} &= \frac{(x - 4)(x + 3)}{(x - 3)(x + 3)}\cdot \frac{3 + x}{4 - x} \\ &= \frac{-(4 - x)(x + 3)(3 + x)}{(x - 3)(x + 3)(4 - x)} \\ &= \frac{-(3+x)}{x - 3} \end{align*}

    Both your answer and the book's answer are wrong.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,661
    Thanks
    1616
    Awards
    1

    Re: raftional expression?

    Quote Originally Posted by zbest1966 View Post
    x2-x-12 . 3+x
    x2-9 4-x

    ans (x-4)(3+X)
    (X-3)(4-X)

    THERE IN THE BOOK IS (3+X)
    (X-3)
    I disagree the answer in the textbook.

    It should be \frac{3+x}{3-x}.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Apr 2012
    From
    bowie md
    Posts
    34

    Re: raftional expression?

    if you a negative on the top you must put a negative on the bottom.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,560
    Thanks
    1425

    Re: raftional expression?

    Quote Originally Posted by zbest1966 View Post
    if you a negative on the top you must put a negative on the bottom.
    Not true. What I have written is correct, I've just written \displaystyle \begin{align*} x - 4 = -(4 - x) \end{align*} so that you have a common factor you can cancel.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: May 1st 2012, 09:54 AM
  2. Replies: 20
    Last Post: January 15th 2012, 09:30 AM
  3. Replies: 6
    Last Post: October 6th 2011, 01:48 PM
  4. It's an expression, right?
    Posted in the Algebra Forum
    Replies: 4
    Last Post: March 26th 2009, 04:00 AM
  5. Expression
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: March 23rd 2009, 03:53 PM

Search Tags


/mathhelpforum @mathhelpforum