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!

Evaluate the limit.

  1. Jan 6, 2008 #1
    1. The problem statement, all variables and given/known data

    Evaluate the Limit.

    lim x -> infinity (3x^3 + x + 26) / (20x^2 - 5x^3)

    2. Relevant equations

    3. The attempt at a solution

    I found the answer to be -3/5. is this correct?
    I just divided the numerator and the denominator by the greatest exponent.
    I see how it was done, but what are the rules to such a problem, and maybe someone could explain what is really going on here. Thankyou.
  2. jcsd
  3. Jan 6, 2008 #2


    User Avatar
    Homework Helper


    to just look and see is the best way. If you wanted, I guess you could have used L'Hopital's Rule:

    f=3x^3 + x + 26
    g=20x^2 - 5x^3

    lim f/g -> inf/inf
    lim f'/g' -> inf/inf
    lim f''/g'' -> inf/inf
    lim f'''/g''' -> -3/5
  4. Jan 6, 2008 #3
    okay i see, but in the original method, do i divide by the largest exponent in the numerator or the denominator, i know I divide the top and bottom by this exponent.
  5. Jan 6, 2008 #4

    Gib Z

    User Avatar
    Homework Helper

    There is a general method for the limit of the quotient of 2 polynomials. Write out the quotient of a general polynomial of degree m, co efficients are a_m, a_{m-1}..., and then divide by another polynomial degree n, co efficients are b_n, b_{n-1}. There are 3 cases, 1) m > n, m=n and m< n. For every case, divide through by the highest exponent of x. What do you get?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Evaluate the limit.
  1. Evaluating Limits (Replies: 1)

  2. Evaluating a limit (Replies: 46)

  3. Evaluate Limit (Replies: 9)

  4. Evaluating limits (Replies: 5)

  5. Evaluate limit (Replies: 3)