Paper 4, Section II, I

Algebraic Geometry
Part II, 2012

Let XX be a smooth projective curve of genus 2, defined over the complex numbers. Show that there is a morphism f:XP1f: X \rightarrow \mathbf{P}^{1} which is a double cover, ramified at six points.

Explain briefly why XX cannot be embedded into P2\mathbf{P}^{2}.

For any positive integer nn, show that there is a smooth affine plane curve which is a double cover of A1\mathbf{A}^{1} ramified at nn points.

[State clearly any theorems that you use.]