Results 1 to 5 of 5

Math Help - Need help with 2 precalc problems...

  1. #1
    Member
    Joined
    Dec 2009
    Posts
    96

    Need help with 2 precalc problems...

    Find and simplify the difference quotient for f(x) = x-7

    (I honestly have no idea what that question is asking for?)

    2. Find (h o g)(2) for g(x)=-3x , h(x)= x^3-2
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member Stroodle's Avatar
    Joined
    Jun 2009
    Posts
    367
    I'm also not sure about the first question, but for the second one:

    h\circ g(x)=h(g(x))

    So you have:

    h(-3x)

    =(-3x)^3-2

    Now plug in 2 in place of x :

    (-3\times2)^3-2

    =-218
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Dec 2009
    Posts
    226
    The difference quotient of the function f(x) is given by \frac{f(x + \Delta x) - f(x)}{\Delta x}.

    If f(x) = x - 7, then f(x + \Delta x) = x + \Delta x - 7.

    Substitute f(x + \Delta x) = x + \Delta x - 7 and f(x) = x - 7 into the difference quotient.

    \frac{f(x + \Delta x) - f(x)}{\Delta x} = \frac{x + \Delta x - 7 - (x - 7)}{\Delta x} = \frac{x + \Delta x - 7 - x + 7}{\Delta x} = \frac{\Delta x}{\Delta x} = 1
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    28
    Quote Originally Posted by Stroodle View Post
    I'm also not sure about the first question, but for the second one:
    Down here in ozzieland I think we would call it, find the derivative using first principles. I also find it tricky to decode some of the questions asked on this forum.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,306
    Thanks
    1282
    Quote Originally Posted by pickslides View Post
    Down here in ozzieland I think we would call it, find the derivative using first principles. I also find it tricky to decode some of the questions asked on this forum.
    Not precisely. Certainly to do that you would need to find the "difference quotient" but it is possible to find the difference quotient ("average rate of change") without taking the limit or finding the derivative. Often such a problem is given as a prelude to introducing the derivative.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Trig/precalc bearing problems need help
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: December 26th 2009, 03:51 AM
  2. precalc
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: February 22nd 2009, 10:17 AM
  3. precalc
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: February 22nd 2009, 01:07 AM
  4. precalc
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: February 21st 2009, 11:21 PM
  5. Precalc
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: August 25th 2008, 03:05 PM

Search Tags


/mathhelpforum @mathhelpforum