The Fitzhugh-Nagumo model for the electrical impulse in a neuron states that, in the absence of relaxation effects, the electrical potential in a neuron v(t) obeys the differential equation

[tex]\frac{dv}{dt} = -v(v^{2} - (1+a)v + a)[/tex]

Where a is some constant such that [tex]0 \ \textless \ a \ \textless \ 1[/tex].
(a) For what values of v is v unchanging (that is, [tex]\frac{dv}{dt} = 0[/tex])?
(b) For what values of v is v increasing?
(c) For what values of v is v decreasing?