B2.10

Algebraic Curves
Part II, 2002

For N1N \geq 1, let VNV_{N} be the (irreducible) projective plane curve VN:XN+YN+ZN=0V_{N}: X^{N}+Y^{N}+Z^{N}=0 over an algebraically closed field of characteristic zero.

Show that VNV_{N} is smooth (non-singular). For m,n1m, n \geq 1, let αm,n:VmnVm\alpha_{m, n}: V_{m n} \rightarrow V_{m} be the morphism αm,n(X:Y:Z)=(Xn:Yn:Zn)\alpha_{m, n}(X: Y: Z)=\left(X^{n}: Y^{n}: Z^{n}\right). Determine the degree of αm,n\alpha_{m, n}, its points of ramification and the corresponding ramification indices.

Applying the Riemann-Hurwitz formula to α1,n\alpha_{1, n}, determine the genus of VnV_{n}.