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How can I show $F:\mathbb{R}^2\rightarrow \mathbb{R}^2$ given by $F(x,y)=(x^3-3xy^2, 3x^2y-y^3)$ is surjective? I've tried solving for $(u,v)=(x^3-3xy^2, 3x^2y-y^3)$ (not solving explicitly, just trying to show solutions exist) but I end up with some square roots that I don't know are real.

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    HINT: Consider $z \rightarrow z^3$ where $z \in \mathbb{C}$. Consider any $(a,b) \in \mathbb{R}^2$ and look at $\sqrt[3]{a+ib}$.2011-11-09
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    Maybe you could check that, e.g., the two functions are neither linearly-dependent from each other, and that they are not both in the same (algebraic) variety.2011-11-09
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    A slight variant of Sivaram: use polar coordinates: $(re^{i\t})^{1/3}=r^{1/3}e^{i2k\pi/3}$ ; select just one of the three roots.2011-11-09

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