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

Limit of multi-variable

  1. Mar 29, 2010 #1
    i need some help with this question

    Find the limit, if it exists, or show that the limit does not exist

    lim(x,y)->(0,0) x2sin2y/(x2+2y2)

    i've tried to x=y x=0 or x=y2 but i still got 0....
  2. jcsd
  3. Mar 29, 2010 #2
    With these kind of exercises, there are two alternatives:

    It could be that the limit does not exist, and then you can prove it by finding two different paths to the origo, such that the limit is different along them.

    Or then, it could be that the limit does exist,and then a one good idea is to use polar coordinates, or in some other way obtain some bounds (upper or lower, whatever you need) as a function of [itex]r[/itex] (distance from origo), and then prove that the bounds converge when [itex]r\to 0[/itex].

    If you don't know in advance what the correct solution is, then you must try both to see what works.

    I believe this expression approaches zero when [itex](x,y)\to 0[/itex], but it could be I made mistake.
  4. Apr 1, 2010 #3


    User Avatar
    Science Advisor
    Homework Helper

    Hi hazellaw! :smile:

    Can you see an easy way of doing it for x2sin2y/(x2 + y2) ?

    Then adapt that. :wink:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook