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!

L'Hospital Rule

  1. Nov 17, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img692.imageshack.us/img692/6661/36979008.jpg [Broken]


    2. Relevant equations



    3. The attempt at a solution
    whats wrong with it? im 100% sure and i can explain each one!
    the first one equals 3 right?

    second one should be true cuz 0/0 can be any number.. (thats what my teacher from high school said at least)
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Nov 17, 2009 #2
    Then you just answered your own question. :-)
     
  4. Nov 17, 2009 #3
    yeah but i guess i think that i know everything but something might be wrong..
    and it will take me a long time to write down an explanation for each one :/

    is the 3rd one right? i mean, f/g has to be g cannot = 0.. but its not in the lhospital rule...
     
  5. Nov 17, 2009 #4
    someone please help me
     
  6. Nov 17, 2009 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    What exactly is your question? In your first post you said "im 100% sure and i can explain each one!"

    The only question I can find is in your second post, "is the 3rd one right? i mean, f/g has to be g cannot = 0.. but its not in the lhospital rule... " In order that we be able to use L'Hospital's rule directly, we must have [itex]\lim_{x\to a} g'(x)\ne 0[/itex] and that's impossible if g'(x)= 0 in some neighborhood of a. We might be able to extend L'Hopital's rule in the case that f'/g' goes to 0/0 itself by using L'Hopital's rule again, but in order for that to work eventually, there must be some nth derivative of g which has non-zero limit at x= a but again, that's impossible if there is some neighborhood of a in which g' is 0.
     
  7. Nov 17, 2009 #6
    my question is, which one from the picture above is wrong?
     
    Last edited: Nov 18, 2009
  8. Nov 18, 2009 #7
    please someone!! i checked it over like 20 times now..
    1. is 'false' for sure cuz it limit = 3
    2. its a fact so 'true'
    3. its a rule so 'true'
    4. its part of the rule so 'true'
    5. small number / big number = closer and closer to 0 ==> 0 so 'true'
    6. limit of infinity = infinity.. :| so 'true'
    7. like the 3rd one but in words, so 'true'

    whats wrong with it??
     
  9. Nov 18, 2009 #8
    point 4. g'(x) must be nonzero in some interval that contains c. This should be:
    in every interval that contains c, g'(x) can't be zero everywhere in that interval.
     
  10. Nov 18, 2009 #9

    jgens

    User Avatar
    Gold Member

    I would reconsider number 6. Just think about what would happen if [itex]\lim_{x \to \infty}f(x) = -\infty[/itex].
     
  11. Nov 19, 2009 #10
    those are such small things that both me and 2 of my buddies didnt pick on.. oh man. :|

    thanks guys
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: L'Hospital Rule
  1. L'Hospital's Rule (Replies: 3)

  2. L'Hospital's Rule (Replies: 3)

  3. L'Hospital's Rule (Replies: 12)

  4. L'hospitals rule (Replies: 5)

  5. L'Hospital's Rule (Replies: 12)

Loading...