- #1
trap101
- 342
- 0
Let f: R2-->R be defined by f(x,y) = xy2/(x2+y2 if (x,y) ≠ 0, f(0,0) = 0
a) is f continuous on R2?
b) is f differentiable on R2?
c) Show that all the dirctional derivatives of f at (0.0 exist and compute them
Attempt:
a) I had an idea to show that multivariate functions are continuous, but now I think it's faulty. I did this:
xy2/(x2+y2 ≤ |xy2|/|(x2+y2| < |xy2|
now taking the lim (x,y)-->(0,0) of |xy2| is 0 as such the function is also continuous.
But looking at a similar example from my notes where the only difference in the function was:
xy2/(x2+y6
We had shown that this was not continuous. So now I'm not so sure if the method I used was valid.
b) I'm a little stumped on showing differentiability in this setting, it doesn't seem to involve using the definition directly because of all the possible paths. So what other option may I have?
This is all in terms of discussing the trouble spot. i.e approaching (0,0)
a) is f continuous on R2?
b) is f differentiable on R2?
c) Show that all the dirctional derivatives of f at (0.0 exist and compute them
Attempt:
a) I had an idea to show that multivariate functions are continuous, but now I think it's faulty. I did this:
xy2/(x2+y2 ≤ |xy2|/|(x2+y2| < |xy2|
now taking the lim (x,y)-->(0,0) of |xy2| is 0 as such the function is also continuous.
But looking at a similar example from my notes where the only difference in the function was:
xy2/(x2+y6
We had shown that this was not continuous. So now I'm not so sure if the method I used was valid.
b) I'm a little stumped on showing differentiability in this setting, it doesn't seem to involve using the definition directly because of all the possible paths. So what other option may I have?
This is all in terms of discussing the trouble spot. i.e approaching (0,0)