Results 1 to 5 of 5

Math Help - function

  1. #1
    Senior Member DivideBy0's Avatar
    Joined
    Mar 2007
    From
    Melbourne, Australia
    Posts
    432

    function

    f)
    If g:[1,a] -> R where g(x) = f(x) and g is one-one, write down the largest possible
    value of a.

    This is part f) of the Q.2, which gives the function -2x^2+5x-3 for x \in [1,\infty)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member DivideBy0's Avatar
    Joined
    Mar 2007
    From
    Melbourne, Australia
    Posts
    432
    Does anyone else think a should be the maximum of f(x)?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,185
    Thanks
    404
    Awards
    1
    Quote Originally Posted by DivideBy0 View Post
    f)
    If g:[1,a] -> R where g(x) = f(x) and g is one-one, write down the largest possible
    value of a.

    This is part f) of the Q.2, which gives the function -2x^2+5x-3 for x \in [1,\infty)
    I'm just a little confused over all of this. Pretend that I haven't done the problem up to this point. What the heck is f(x) anyway? Are you saying f(x) = -2x^2 + 5x - 3?

    You have g: [1, a] \to \mathbb{R}: g(x) = f(x). You know that g is one-to-one.

    So the question is really: Given the restriction of the domain of f to [1, a], what is the largest value of a such that f(x) is one-to-one.

    If your f(x) = -2x^2 + 5x - 3 then it looks like x = 1 is on the left of the vertex, so a would have to be the x coordinate of the vertex of f(x). (That's the accurate way to say what I think you were trying to say.)

    -Dan
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,924
    Thanks
    1762
    Awards
    1
    Quote Originally Posted by DivideBy0 View Post
    Does anyone else think a should be the maximum of f(x)?
    Yes that is the correct answer.
    An easy to see it is to simlpy graph the function.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Senior Member DivideBy0's Avatar
    Joined
    Mar 2007
    From
    Melbourne, Australia
    Posts
    432
    Quote Originally Posted by topsquark View Post
    I'm just a little confused over all of this. Pretend that I haven't done the problem up to this point. What the heck is f(x) anyway? Are you saying f(x) = -2x^2 + 5x - 3?
    Thanks both of you
    I too was a bit confused over its ambiguity. It didn't say that -2x^2+5x-3 was f(x), so I guess it had to be assumed.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 20
    Last Post: November 27th 2012, 06:28 AM
  2. Replies: 0
    Last Post: October 19th 2011, 05:49 AM
  3. Replies: 4
    Last Post: October 27th 2010, 06:41 AM
  4. Replies: 3
    Last Post: September 14th 2010, 03:46 PM
  5. Replies: 2
    Last Post: September 2nd 2010, 11:28 AM

Search Tags


/mathhelpforum @mathhelpforum