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Stability is determined by the direction of the vector field, which is given by the sign of $dz/dt$. Near $z = -2$ and $z = 2$, the arrows on the phase line point toward these equilibria, meaning nearby trajectories converge to them, making them stable.

Conditions: The system is a one-dimensional autonomous ODE.; Stability is inferred from the sign of $dz/dt$ on intervals adjacent to the equilibria.

Stability is determined by the direction of the vector field, which is given by the sign of $dz/dt$. Near $z = -2$ and $z = 2$, the arrows on the phase line point toward these equilibria, meaning nearby trajectories converge to them, making them stable.

Conditions: The system is a one-dimensional autonomous ODE.; Stability is inferred from the sign of $dz/dt$ on intervals adjacent to the equilibria.