Skip to main content
\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)
Mathematics LibreTexts

B: Fields

  • Page ID
    2103
  •  

    \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

    \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

    Definition

    A \(\textit{field}\) \(\mathbb{F}\) is a set with two operations \(+\) and \(\cdot\), such that for all \(a, b, c \epsilon \mathbb{F}\) the following axioms are satisfied:

    • A1. Addition is associative \((a + b) + c = a + (b + c)\).
    • A2. There exists an additive identity \(0\).
    • A3. Addition is commutative \(a + b = b + a\).
    • A4. There exists an additive inverse \(-a\).
    • M1. Multiplication is associative \((a \cdot b) \cdot c = a \cdot (b \cdot c)\).
    • M2. There exists a multiplicative identity \(1\).
    • M3. Multiplication is commutative \(a \cdot b = b \cdot a\).
    • M4. There exists a multiplicative inverse \(a^{-1}\) if \(a \neq 0\).
    • D. The distributive law holds \(a \cdot (b + c) = ab + ac\).

    Note

    Roughly, all of the above mean that you have notions of \(+, -, \times, \div\) just as for regular real numbers.

    Fields are a very beautiful structure; some examples are rational numbers \(\mathbb{Q}\), real numbers \(\mathbb{R}\), and complex numbers \(\mathbb{C}\). These examples are infinite, however this does not necessarily have to be the case. The smallest example of a field has just two elements, \(\mathbb{Z}_2 = {0, 1}\) or \(\textit{bits}\). The rules for addition and multiplication are the usual ones save that $$1 + 1 = 0.$$

    Contributor