1. find the limit

how do I find the limit of the following two?

1. limit of xyz/(x^3+yz^2) as (x,y,z) goes to (0,0,0)

2. limit of (x+y)/(sqrt.(x^2+y^2)) as (x,y,z) goes to (0,0,0)

2. Neither of these limits exist. For the first, try following the path $x = at, y= bt, z = ct$ and the second $y = mx, z=0$.

3. I made a simple mistake. The second one is as (x,y) goes to (0,0). Is the answer still the same?

4. Yes, just omit the $z$.