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

Homework Help: Limits with three variables (a different problem)

  1. Oct 14, 2008 #1
    1. The problem statement, all variables and given/known data

    the limit as (x,y)->0,0 of (x^2+y^2)ln(x^2+y^2)
    (Hint: as (x,y)->(0,0) r->0(from the right)

    2. Relevant equations

    3. The attempt at a solution

    I converted to polar coordinates then used trig identities and eventually got to the limit of r->0(from theright) of r^2 * (ln(r^2)) I eventually got this limit to equal 0. I'm pretty sure to make sure the limit exists I have to evaluate it as r->0 (from the left) as well but I'm not sure how...
  2. jcsd
  3. Oct 14, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    You only need to evaluate the limit of r from one direction, as r is a variable that is always non-negative. Remember it represents a radius, ie a positive number.
  4. Oct 14, 2008 #3
    ohhhh I see thanks
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook