Results 1 to 5 of 5

Math Help - algebra??

  1. #1
    Member
    Joined
    Jan 2008
    Posts
    83

    algebra??

    http://img165.imageshack.us/img165/8938/algos7.jpg

    i get: x^2-2x-8=0
    (x-4)(x+2)=0


    ?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by algebra2 View Post
    You need to show your working - all of it. It's impossible to see the errors you've made and the misunderstandings you most likely have.

    Here're some things to consider:

    f(x + 2) = (x + 2)^2 - 2(x + 2) = expand and simplify.

    f(2) = 0.

    Therefore f(x + 2) - f(2) = .......

    Therefore \frac{f(x + 2) - f(2)}{x} = \frac{........}{x} = x + 2.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Jan 2008
    Posts
    83
    first i did:

    x^2-2x(x+2) - 2x^2-4x / x

    second i did:

    x^3 + 2x^2- 2x^2 - 4x - 2x^2 - 4x

    third i simplified and got:

    x^3 - 2x^2 - 8x / x

    then i divided it all by x and got:

    x^2 - 2x - 8

    then i set it up with 0:

    x^2 - 2x - 8 = 0

    finally i put it into this form:

    (x-4)(x+2) = 0


    sorry, but i am bewildered with what you got and how you got it. could you please show step by step how you got that?
    Last edited by algebra2; January 13th 2008 at 05:36 PM. Reason: Not Applicable
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by algebra2 View Post
    first i did:

    x^2-2x(x+2) - 2x^2-4x / x

    second i did:

    x^3 + 2x^2- 2x^2 - 4x - 2x^2 - 4x

    third i simplified and got:

    x^3 - 2x^2 - 8x / x

    then i divided it all by x and got:

    x^2 - 2x - 8

    then i set it up with 0:

    x^2 - 2x - 8 = 0

    finally i put it into this form:

    (x-4)(x+2) = 0
    Oh, I see. Lucky you replied.

    I now know exactly what your misunderstanding is. It's a bad one. But maybe simple to fix. Read the following very carefully.

    f(x+2) does NOT mean f times (x + 2), that is, f(x + 2) does NOT mean (x^2 - 2x) (x + 2) .......

    If f(x) = x^2 - 2x, then I hope we can agree that f(a) = a^2 - 2a, f(b) = b^2 - 2b etc. f(apple) = (apple)^2 - 2(apple) etc. Do you see how it works? You replace the x in the rule with whatever is in ().

    f(x + 2) = (x + 2)^2 - 2(x + 2). I have replaced x in the rule with (x + 2).

    Then f(x + 2) = x^2 + 4x + 4 - 2x - 4 = x^2 + 2x.

    Similarly, f(2) does not mean f times 2. f(2) = 2^2 - 2(2). I have replaced x in the rule with 2.

    It is essential that you revise functional notation and what it means or you are in for a world of pain .....
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Jan 2008
    Posts
    83
    oh now i see.

    so its: (x+2)(x+2) - 2(x+2) / x

    = x^2 + 4x + 4 - 2x - 4 - 2^2 - 4 / 2
    = x^2 + 2x / x

    divide the x and i get "x+2"

    thanks for clearing things up.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: February 4th 2011, 09:39 AM
  2. Replies: 2
    Last Post: December 6th 2010, 04:03 PM
  3. Algebra or Algebra 2 Equation Help Please?
    Posted in the Algebra Forum
    Replies: 4
    Last Post: May 12th 2010, 12:22 PM
  4. Replies: 0
    Last Post: April 24th 2010, 12:37 AM
  5. algebra 2 help
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 4th 2009, 07:24 PM

Search Tags


/mathhelpforum @mathhelpforum