Chapter 7.1, Problem 1E

Interpretation Introduction

Interpretation:

To sketch the portrait for the system equation ${\dot{\text{r}}\text{ = r}}^3\text{ - 4r, }\dot{\theta }\text{ = 1}$, where $\text{r}$ and $\theta$ are polar co-ordinates.

Concept Introduction:

Fixed points are the points where $\dot{\text{r}}\text{ = 0}$.

If $\text{r*}$ is the fixed point of the system, then all stable trajectories inside the circle $\text{r*}$.