To "fill in" the space between two curves (in this example, f(x) = sin(x)-2 and g(x) = 3-x^2) do the following:
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[*]Define your two functions.
[*]Use the SURFACE command: Surface[ t , u f(t) + (1 - u) g(t) , 0 , t , x(A) , x(B) , u , 0 , 1 ]
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Once you do this, you should be able to change f(x) and g(x) and the surface should update accordingly!
