# State Equation of negative resistance from current source

I have to find the state equation from the circuit, the problem is, on the node with red marker. Here is what I've done

$$\u = I_C+I_R\$$

$$\u = C\frac{dV}{dt} + \frac{V}{R}\$$

and if the value from components is included, then

$$\u = \frac{dV}{dt} - V\$$ (because of negative resistance)

is this right? based on the solution given, it should be

$$\u = \frac{dV}{dt} + V\$$

is the negative in resistance is ignored?