An embedding of a number field $K$ is a field homomorphism $K\to \C$. A number field of degree $n$ has $n$ distinct embeddings, which may be distinguished as real or complex depending on whether the image of the embedding is contained in $\R$ or not.
Complex embeddings necessarily come in conjugate pairs. The signature of a number field is determined by the number of real embeddings and the number of pairs of conjugate complex embeddings.
For $K=\Q(a)$, where $a$ is an algebraic number with minimal polynomial $f(X)$, each embedding $\iota$ is uniquely determined by the value $z=\iota(a)$, which is one of the complex roots of $f(X)$. The embedding is real if $z\in\R$ and complex if $z\notin\R$.
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- Last edited by Andrew Sutherland on 2024-11-08 18:54:06
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- 2024-11-08 18:54:06 by Andrew Sutherland (Reviewed)
- 2023-03-02 16:06:16 by John Cremona (Reviewed)
- 2018-09-29 16:59:03 by Andrew Sutherland (Reviewed)