Hi. :)

I have this one in my textbook.

It is really hard!!!

I can't do anything.

Problem:

For what values of the number r is the function

$\displaystyle f(x,y,z)=\frac{(x+y+z)^r}{x^2+y^2+z^2} \,$ if $\displaystyle \, (x,y,z) \neq 0$

$\displaystyle f(x,y,z) = 0 \,$ if $\displaystyle \, (x,y,z)=0$

continuous on R ?

the problem here is that the question did not specify r, is it natural or real .. etc