(a)

> f := subs( y(t)=y, rhs(MODEL) );

> plot( f, y=-3..3, dydt=-10..10, discont=true );

>

The important thing to note from this plot is that the ODE

- has equilibria at and (and a singularity at )

- has solutions that are increasing for < -1, 1 < < 2, and > 2

- has solutions that are decreasing for -1 < < 1

From these observations the phase line is easily drawn.