Dear Geoff
You asked:

>For #2, can we do either a 2D or 3D picture?  
Yes, but since the problem requests a 3D picture, you should say that 
you're doing a 2D picture instead, because your 3D picture is not 
good enough.
 
>For #3, how exactly are we supposed to describe the surfaces? Is it okay
>to say for part a (u=x^2+y^2+z^2) that x, y, and z may be any number but
>u>=0? I'm just a little confused on how we're supposed to describe it.
 
Yes, that's a start but it's not very useful. 
So, check out what it does look like for u = 1? Restrict further, 
and draw its intersection with the three walls in the "corner of a room"
sketch. Finally, can't you guess what u=1 looks like? You see at least 
one every day!

>For #5, do we just show that there's a gap at point (0,0)?

Sorry, I don't have my book handy. When you ask for help, please give
me enough of a clue. But as for indicating a "gap" at a point, e.g.
the surface is not defined there. You can draw a little open circle 
and label it "not there" or something like that. Missing lines and 
curves can be similarly drawn double and labeled. Missing planes
or surfaces .... well just draw them and say they're not in the 
region to be described.

OK ?


:wq!