1. Not finding help here? Sign up for a free 30min 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!

Combining f(x) and g(x)?

  1. Dec 1, 2009 #1
    1. The problem statement, all variables and given/known data

    Apologies for any trouble, but I'm not going to post any numbers, as my school is very sensitive about plagiarism and the like in homework. I only need some help in figuring out what to do.

    I'm given a table of x values 1 to 5, and for each, corresponding y-values for two functions: f(x) and g(x). So my table has three rows x, f(x), and g(x).

    I have to find the limit of [2f(x) - 3g(x)] as x approaches 1.

    I can do g(f(x)), but... Af(x) - Bg(x)? What...?

    I know limits are calculus stuff, but what I really need help with here is manipulating g(x) and f(x), and that should be precalculus... right?

    2. Relevant equations
    None that I know of

    3. The attempt at a solution
    I'm stumped. The first thing that did cross my mind was substituting the y values I'm given from the table into f(x) and g(x), but... that can't be right! I get a number that makes no sense.
     
  2. jcsd
  3. Dec 1, 2009 #2
    I fail to see the problem. [2f(x) - 3g(x)] doesnt involve compound functions.
     
  4. Dec 1, 2009 #3
    Hmm, so should I just post this in the calculus forum? I just don't know how to find the limit of [2f(x) - 3g(x)] as x approaches 1.
     
  5. Dec 2, 2009 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    [tex]\lim_{x\to a} (Af(x)+ Bg(x))= A(\lim_{x\to a} f(x))+ B(\lim_{x\to a} g(x))[/tex]

    I would think you would have learned that well before
    [tex]\lim_{x\to a} f(g(x))[/tex]
     
  6. Dec 2, 2009 #5
    Ah, thank you so much!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook