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!

Homework Help: Rigorous Multivariable Limit Definition Problem

  1. Aug 26, 2016 #1
    1. The problem statement, all variables and given/known data
    Hey I'm trying to prove the rigorous definition of limit for the following function:
    Lim (x,y) approaches (1,1) of f(x,y)=(y*(x-1)^(4/3))/((x/1)^2+abs(x)*y^2)

    2. Relevant equations
    abs(x^2)<abs(x^2 +y^2)

    3. The attempt at a solution
    I know the rigorous definition of limit. I tried to constraint the denominator by eliminating one of the terms since both are greater than zero, however, I was left with what seemed like terms that could not be constrained. I never really done a rigorous definition of limit that's not centered on (0,0). I would appreciate some help.
  2. jcsd
  3. Aug 26, 2016 #2
    If you feel more comfortable with limits centred at ##(0,0)##, you can deform the problem (in order to get an idea for ##\delta##), by doing a shift ##(x,y)\rightarrow (x-1,y-1)##. I'm assuming proofs are required to be directly from the ##\epsilon##-##\delta## definition?
  4. Aug 26, 2016 #3


    Staff: Mentor

    Typo above? Should the (x/1)^2 be (x - 1)^2?
  5. Aug 27, 2016 #4
    Yes, that is in fact a typo.
  6. Aug 27, 2016 #5
    That's right, however I may constraint the whole thing backwards, that is, work from ε and thereafter find δ in the form of ||(x,y)-(v,w)|| inside the ε I am constraining.(which in the definition of the limit is |f(x,y)-L|<ε L being the Limit I am trying to prove)... I'm not sure how much sense that made, let me know if you need any more clarification. The course is not in english, as you might have noticed.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted