Plot an isosurface of a function depending on three variables

Dear all,

I have a question about plotting a specific surface (in 3D) or line (in 2D). As i have a function f with three symbolic variables x,y, and z, f(x,y,z), I would like to plot the surface where the combination of variables gives a function value equal to zero. The range of the symbolic variables are known.

x = [10,50];

y=[5,100];

z=[100,300];

I already tried the "contourf" function, but i do not get the required result.

Does anybody have any suggestion ?

Thanks in advance.

[KSSV]

How the function f(x,y,z) is defined? You have not shown us the function.

[Abdelmajid Ben yahya]

It is quit a large function. That is why I converted my specific question to a more general one.

If you want to see how the function looks you can find in attachment. The three variables are in my case a,b and h.

The boundaries of the three variables are the following:

a=[30,100]

h=[40,160]

b=[200,360]

Thank you for your fast respons.