Galois Theory - 1998

This text offers a clear, efficient exposition of Galois Theory with complete proofs and exercises. Topics include: cubic and quartic formulas, Fundamental Theory of Galois Theory; insolvability of the quintic; Galois's Great Theorem (solvability by radicals of a polynomial is equivalent to solvability of its Galois Group); and computation of Galois groups of cubics and quartics. There are appendices on group theory, ruler-compass constructions, and the early history of Galois Theory. This book provides a concise introduction to Galois Theory suitable for first-year graduate students, either as a text for a course or for study outside the classroom. This new edition has been completely rewritten. Proofs are now clearer because more details are given and because the exposition has been reorganized (for example, the discussion of solvability by radicals now appears later in the book). The book now begins with a short section on symmetry groups of polygons in the plane, for there is an analogy between symmetry groups of polygons and Galois groups of polynomials. This analogy can serve as a guide to help readers organize the theoretic definitions and constructions. Several new theorems have also been included; for example, the Casus Irreducibilis.