- #1

Settembrini

- 5

- 0

[itex]\frac{-y}{ x^{2}+y ^{2} } + \frac{x}{ x^{2}+y ^{2}}y'=0[/itex]

is not exact in [itex]\mathbb{R^{2}} \setminus \{(0,0)\}[/itex].

It's obvious that I have to use the fact, that the set is not simply connected, but I don't know how to do it.