- #1

spitz

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## Homework Statement

I have:

[itex]\dot{x}=4x+y-x(x^2+y^2)[/itex]

[itex]\dot{y}=4y-x-y(x^2+y^2)[/itex]

And I need to find [itex]\dot{r}[/itex] and [itex]\dot{\theta}[/itex]

**2. The attempt at a solution**

I got as far as:

[itex]\dot{x}=r(\text{sin}(\theta)-\text{cos}(\theta)(r^2-4))[/itex]

[itex]\dot{y}=r(-\text{sin}(\theta)(r^2-4)-\text{cos}(\theta))[/itex]

How do I go from here to [itex]\dot{r}[/itex] and [itex]\dot{\theta}[/itex] ?

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