Answered
When I enter b(x, y) = x² + y² into the input line I see a paraboloid around the z-axis, and it is classified as a Multivariable Function. However, I get identical graphs when I enter
c(x, z) = x² + z² and d(y, z) = y² + z².
I expected to get paraboloids around each of the axes but that is not the case. Why is this?
The same question 
Hi tpgettys!
I think that the name of the two variables are always interpreted as x- and y-value.
If you type f(a,b)=a²+b² you will get the same picture, because the first variable a is dedicated to x and the second b is dedicated to y and so the function-value is always dedicated to z.
So if you want to have a paraboloid around the y-axis you can use the surface-command
note that x, y, z are not allowed as variables, but I think, they rename it internal if you use them: https://wiki.geogebra.org/e...
or an equation like
Kind regards
mire2
Hi mire2, and thanks for your reply.
I understand that x, y and z are not allowed in the Surface() command, which seems to suggest that those letters are dedicated to specific usage.
In the 2D window if you enter f(y)=2*y you will get an error; x just be used for the independent variable. This difference should be documented somewhere, as it a source of great confusion (at least in my mind!), but I have not run across it yet.
another solution:
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