# B3.3 Algebraic Curves - Material for the year 2020-2021

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Part A Topology. Introduction to Manifolds would be useful but not essential. Projective Geometry is recommended. Also, B3.2 (Geometry of Surfaces) is helpful, but not essential.

16 lectures

### Assessment type:

- Written Examination

A real algebraic curve is a subset of the plane defined by a polynomial equation $p(x,y)=0$. The intersection properties of a pair of curves are much better behaved if we extend this picture in two ways: the first is to use polynomials with complex coefficients, the second to extend the curve into the projective plane. In this course projective algebraic curves are studied, using ideas from algebra, from the geometry of surfaces and from complex analysis.

Students will know the concepts of projective space and curves in the projective plane. They will appreciate the notion of nonsingularity and know some basic features of intersection theory. They will view nonsingular algebraic curves as examples of Riemann surfaces, and be familiar with divisors, meromorphic functions and differentials.

Projective spaces, homogeneous coordinates, projective transformations.

Algebraic curves in the complex projective plane. Irreducibility, singular and nonsingular points, tangent lines.

Bezout's Theorem (the proof will not be examined). Points of inflection, and normal form of a nonsingular cubic.

Nonsingular algebraic curves as Riemann surfaces. Meromorphic functions, divisors, linear equivalence. Differentials and canonical divisors. The group law on a nonsingular cubic.

The Riemann-Roch Theorem (the proof will not be examined). The geometric genus. Applications.

- F. Kirwan,
*Complex Algebraic Curves*, Student Texts 23 (London Mathematical Society, Cambridge, 1992), Chapters 2-6. - W. Fulton,
*Algebraic Curves*, 3rd ed., downloadable at http://www.math.lsa.umich.edu/~wfulton