How do you find a level surface representing another surface?

[shalanheyyo]

Homework Statement

The surface S is the graph of f(x,y) = sqrt(25-x^2)

a)Find a level surface g(x,y,z) = c Representing S.
b) with C=?

Homework Equations

The Attempt at a Solution

I have no idea what to do with this question. How should I find g(x,y,z)? Do I let sqrt(25-x^2) = C? I tried this method and the answer is wrong. Am I on the right track?And what does it mean by C=?

 

[Simon Bridge]

http://math.arizona.edu/~calc/Text/Section12.5.pdf
... but surely you've covered this?

Don't know what it means by C=?
Does not look like a general notation.

 

[shalanheyyo]

http://math.arizona.edu/~calc/Text/Section12.5.pdf
... but surely you've covered this?

Don't know what it means by C=?
Does not look like a general notation.

I missed 2 weeks of lectures because I was sick, so I am having a really difficult time to catch up...
So basically I take sqrt(25-x^2)-z and solve it for Z?

 

[Simon Bridge]

Ah - then you should read through that link I gave you.
It is very hard to give you hints without doing the thing for you it's that basic - the link covers the concepts and has examples.

Basically, you put g(x,y,z) = z-f(x,y) = c which gives you a family of 3D surfaces... now, if c=0, you get a simplification that will tell you the basic shape of the surface in 3D.

 

[HallsofIvy]

First, f(x,y)= \sqrt{25- x^2} is not a surface in a xyz-coordinate system because you need a coordinate representing z. Rather z= \sqrt{25- x^2} is a surface. And that is the same as \sqrt{25- x^2}- z= 0.

 

[Simon Bridge]

Its badly phrased isn't it?
I got my interpretation by googling for similar phrasing ... JIC.
shalanheyyo really needs to check with someone else on the course.

It could be the intent is that one put z=f(x,y) then rearrange that so all the "constant" terms are on the RHS and all the terms with x or y or z in them are on the LHS. This would have form g(x,y,z)=c, and it would make sense to ask what c is.

 

[shalanheyyo]

I emailed my Prof and the question is actually really simple. I guess I got confused by how the question is worded

 

[Simon Bridge]

So are you going to enlighten us?