Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What does lim=infinity mean?

  1. Oct 21, 2007 #1
    I can't believe I'm asking this, because I should know this answer but I'm now doubting myself.

    If a function goes to infinity as x approaches some real number, would we say the limit as x approaches that number is infinity or would we say that it does not exist?

    Doesn't the limit always have to be a real number, but infinity isn't one?

    So for example:
    the limit as x approaches 0 from the right of 1/x is infinity or not defined?
  2. jcsd
  3. Oct 21, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    It is a question of whether you are in the reals or the extended reals. The latter includes infinity.
  4. Oct 21, 2007 #3
    Generically people will say the limit equals infinity. Indeed infinity is not a real number, but it is useful to use the shorthand of saying the limit equals infinity, as this is more specific than just saying that the limit is undefined.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook