1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Trying to understand rewritten equation

  1. May 2, 2012 #1

    I am hoping someone can help me understand something. I was watching one of the MIT OCW videos and it ran through the following

    Δf/Δx = (1/(x0x - 1/x0)) / Δ0

    can be rewritten as

    Δf/Δx = 1/Δx (x0-(x0x) / (x0x)x0)

    But I am not sure how this was done.

    I hope someone can help me with this.

    Thanks in advance.

  2. jcsd
  3. May 2, 2012 #2


    Staff: Mentor

    What you wrote above is very confusing. I believe that what you saw looked more like this:

    Δf/Δx = (1/(x0+Δx) - 1/x0)) / Δx

    Using LaTeX makes it even clearer.
    $$Δf/Δx = \frac{\frac{1}{x_0 + Δx} - \frac{1}{x_0}}{Δx}$$

    What is apparently happening is that they are finding the derivative of f(x) = 1/x, at the point x0.

    The key to simplifying the above is being able to combine 1/(x0 + Δx) and 1/x0. To do this, find the common denominator and combine the two terms using that denominator.

  4. May 2, 2012 #3

    And thanks for the reply.

    Yea, sorry about writing it like I did ..I am not too familiar with LaTeX.

    Well, the common denominator is x0, which will give the x0-(x0x)
  5. May 2, 2012 #4


    Staff: Mentor

    No, the common denominator is NOT x0.

    If you had to add 3/5 and 1/(5 + 3) would you say that the common denominator was 5?
  6. May 2, 2012 #5


    Staff: Mentor

    Mod note: Moved from Precalc section.
    Last edited: May 2, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook