Results 1 to 2 of 2

Thread: Derivative Quiz Tomorrow

  1. #1
    Sep 2008

    Derivative Quiz Tomorrow

    Hey all, just doing some homework in preparation for the quiz tomorrow (well,'s in 4 hours).

    Running into trouble with using limits to compute derivatives.

    Here are the problems:

    Use limits to compute the following derivatives:

    1. $\displaystyle f'(3)$ where $\displaystyle f(x)=\frac{1}{2x-5}$

    Pretty sure limit here is zero, but I do not understand how I would visualize this with much harder equations...

    2. $\displaystyle f'(2)$ where $\displaystyle f(x)=x^3$

    3. $\displaystyle f'(4)$ where $\displaystyle f(x)=\sqrt{2x-1}$

    Also confused about questions asking to compute limits that involve infinity:
    1. $\displaystyle \lim_{x \to \infty}\frac{1}{x^2}$

    2. $\displaystyle \lim_{x \to \infty}\frac{5x+3}{3x-2}$

    3. $\displaystyle \lim_{x \to \infty}\frac{x^2+x}{x^2-1}$

    Read the textbook a few times but cannot seem to grasp it... Would appreciate some help or at least a guide that is easy to comprehend.

    Another concern is the +'s and -'s atop of infinity. As far as I understand, these signify which direction to count the limit from. Anymore help would be greatly appreciated!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Aug 2008

    Hope this helps

    Hi VX-1

    Finding solutions to the derivatives 2 and 3 isn't difficult but if you're being asked to solve them using limits thats a different story, the thing I used to do when solvin limits was substitute x - infinity with x = a very large number;

    For example 1.

    if we think of x being a very large number say 100000, then substitute it and solve it the answer is 1x10^-10 or effectively zero, we can say as x tends to infinity the limit is zero. (even though it is impossible to really divide by infinity)

    For question 2 we have a very large number divided by a very large number, adding 3 or subtracting 2 would have a negligible effect, the answer is close enough to 1 that we can say the limit is one.

    Hope that helped, good luck for your quiz
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Factoring Polynomials - quiz tomorrow!
    Posted in the Algebra Forum
    Replies: 2
    Last Post: Dec 14th 2008, 02:53 PM
  2. Replies: 4
    Last Post: Dec 9th 2008, 08:29 PM
  3. Replies: 1
    Last Post: May 22nd 2008, 08:33 PM
  4. Derivative Quiz Bonus
    Posted in the Calculus Forum
    Replies: 6
    Last Post: Jan 2nd 2008, 08:42 PM
  5. Replies: 3
    Last Post: Apr 4th 2006, 04:27 AM

Search Tags

/mathhelpforum @mathhelpforum