# Algebraic extension

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2010 Mathematics Subject Classification: Primary: 12F [MSN][ZBL]

A field extension \$K/k\$ in which every element of \$K\$ is algebraic over \$k\$; that is, every element of \$K\$ is the root of a non-zero polynomial with coefficients in \$k\$. A finite degree extension is necessarily algebraic, but the converse does not hold: for example, the field of algebraic numbers, the algebraic closure of the field of rational numbers, is an algebraic extension but not of finite degree.

Algebraic extensions form a distinguished class : that is, they have the properties (i) for \$M / L / K\$ we have \$M/L,\,L/K\$ algebraic if and only if \$M/K\$ is algebraic; (ii) \$M / K,\,L/K \$ algebraic implies \$ ML/L\$ algebraic.

An extension which is not algebraic is a transcendental extension.

#### References

 [b1] Paul J. McCarthy, "Algebraic Extensions of Fields", Courier Dover Publications (2014) ISBN 048678147X Zbl 0768.12001 [b2] Steven Roman, Field Theory, Graduate Texts in Mathematics 158 (2nd edition) Springer (2007) ISBN 0-387-27678-5 Zbl 1172.12001
How to Cite This Entry:
Algebraic extension. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Algebraic_extension&oldid=42117