Hi thanks for your anwers, yes I1 is an inductor,
I1=integral of (Va-V1)/L, but in all this equations where i use the resistor R, i think R is part of I1, but i don't know how write the equation in this case.
Here is the original exercise, 5.15
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Homework Statement
Using nodal analisis we need obtain the differential equation
2. The attempt at a solution
For I1 and take the point under C as reference, but i am stuck on it