Question: Parametric plot3d

Hello,

I have two function :

And

 

A={g(R,L)=1}=

(I will call that L : L0=h(R))

 

 

So I want to represent f(A) in 3D

So I tried 

It does not work, and I do not see how I could do otherwise...

 

Thank's in advance !

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