# Section 9.1

**1.**6.1.14**2.**6.1.16**3.**6.1.19**4.**6.1.13**5.**6.1.12**6.**6.1.18**7.**6.1.15**8.**6.1.17**9.**Equilibrium solutions $x(t)\equiv 0,\text{}\pm 2$. The critical point (0, 0) in the phase plane looks like a center, whereas the points $(\pm 2,\text{}0)$ look like saddle points.**10.**Equilibrium solution $x(t)\equiv 0$. The critical point (0, 0) in the phase plane looks like a spiral sink.**11.**Equilibrium solutions $x(t)\equiv \dots ,-2\pi ,-\pi ,\text{}0,\text{}\pi ,\text{}2\pi ,\dots $. The phase portrait shown in the solutions manual suggests that the critical point $(n\pi ,\text{}0)$ in the phase plane is a spiral sink if`n`is even, but ...

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