I am working on an Isoperimetric problem.

I have two différential dL and dA. And I am seeking the function y for wich the two différentials are collinear.

So I want "dL/dA=constant"

I tried many expression, but I don't know how to express the "= constant"
I tried also (dL/dA)'=0 but no workable answer...

Thank's for your help !

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 !