Results 1 to 6 of 6

Thread: Finding the Derivative by Limit Process

  1. #1
    Member
    Joined
    Apr 2009
    Posts
    96

    Finding the Derivative by Limit Process

    I have the function:
    $\displaystyle f(x)=5x+6$

    I need to "find the derivative by the limit process".

    Using:
    $\displaystyle (f(x+deltax)-f(x))/deltax$

    My work:
    $\displaystyle (5(x+deltax)+6-(5x+6))/deltax$

    $\displaystyle (5x+5deltax+6-(5x+6))/deltax$

    The two 5x's go away, the 5Δx and Δx go away, so I'm left with 12, which isn't the answer.

    I'm lost.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,237
    Thanks
    33
    $\displaystyle =\lim_{h\to 0 }\frac{f(x+h)-f(x)}{h}$

    $\displaystyle =\lim_{h\to 0 }\frac{5(x+h)+6-(5x+6)}{h}$

    $\displaystyle =\lim_{h\to 0 }\frac{5x+5h+6-5x-6}{h}$

    $\displaystyle =\lim_{h\to 0 }\frac{5h}{h}$

    $\displaystyle =\lim_{h\to 0 }5$

    $\displaystyle =5$
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Apr 2009
    Posts
    96
    Thanks a lot. I need to start using $\displaystyle h$ instead of Δx, since Δx is pretty confusing.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,237
    Thanks
    33
    I agree with this.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Apr 2009
    Posts
    96
    New question...


    There's just way too many things on my paper and I'm just lost now .
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,237
    Thanks
    33
    This one will take some doing, here's the first bit, now gettting expanding!

    $\displaystyle =\lim_{h\to 0 }\frac{\left(9(x+h)^2-3(x+h)-\frac{3}{(x+h)^2}\right)-\left(9x^2-3x-\frac{3}{x^2}\right)}{h}$
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 4
    Last Post: Feb 2nd 2010, 09:07 AM
  2. Replies: 3
    Last Post: Jan 18th 2010, 10:44 AM
  3. Replies: 4
    Last Post: Nov 19th 2009, 11:43 AM
  4. Finding derivative from limit definition
    Posted in the Calculus Forum
    Replies: 2
    Last Post: May 29th 2009, 08:40 PM
  5. Finding limit/derivative
    Posted in the Calculus Forum
    Replies: 9
    Last Post: Mar 26th 2008, 04:39 AM

Search Tags


/mathhelpforum @mathhelpforum