Math 2.0

Field theory and polynomials Proof

Proof that the multiplicative group of a finite field is cyclic

Builds on Finite fieldGroup of units of a ringFinite subgroups of the multiplicative group of a field are cyclic

Proof

  1. Let FF be a finite field of order qq, and let F×F^\times be its group of units.
  2. In a field, every nonzero element is a unit. So F×=F∖{0}F^\times = F \setminus \set{0} has q−1q - 1 elements.
  3. So F×F^\times is a finite subgroup of the multiplicative group of the field FF.
  4. By the theorem on finite subgroups of K×K^\times, with K=FK = F and G=F×G = F^\times, the group F×F^\times is cyclic.
  5. By step 2, it is cyclic of order q−1q - 1.

Idea

The whole group F×F^\times is itself a finite subgroup of the multiplicative group of FF. So the general theorem applies to it directly.

Reading path

To understand this page from the ground up, read these 139 pages in order. The foundations come first. The path takes the proofs Proof of Bézout's identity, Proof of cancellation in an integral domain, Proof of the generalized Euclid's lemma, Proof of the commutativity of addition by induction, Proof that equivalence classes form a partition, Proof that g to the n equals 1 iff the order divides n, Proof that R[x] is an integral domain iff R is, Proof that g to the order of the group is the identity, Proof that finite subgroups of the multiplicative group of a field are cyclic, Proof that the order of an element divides the order of the group, Proof of the degree of a product over an integral domain, Proof of strong induction from ordinary induction, Proof of the laws of exponents in a group, Proof that a product of two finite cyclic groups is cyclic iff their orders are coprime, Proof that a polynomial over a field has at most as many roots as its degree, Proof of the remainder theorem, Proof that a finite abelian group is cyclic iff its exponent equals its order, Proof that the order of a cyclic subgroup equals the order of its generator, Proof of the well-ordering principle from strong induction, Proof of the division algorithm, Proof of the uniqueness of inverses, Proof that cyclic groups of the same order are isomorphic, Proof of Lagrange's theorem, Proof of the factor theorem, Proof that cosets have the same cardinality as the subgroup.

  1. Binary operation definition
  2. Definition by recursion concept
  3. Divisibility definition
  4. Element definition
  5. Group concept
  6. Left coset concept
  7. Mathematical induction concept
  8. Natural numbers object
  9. Peano axioms concept
  10. Proposition concept
  11. Vector space definition
  12. Commutativity definition
  13. Identity element definition
  14. Greatest common divisor definition
  15. Set definition
  16. Direct product of groups definition
  17. Group homomorphism definition
  18. Order of a group definition
  19. Ring definition
  20. Subgroup definition
  21. Successor function definition
  22. Conjunction definition
  23. Disjunction definition
  24. Implication definition
  25. Predicate definition
  26. External direct sum definition
  27. Inverse element definition
  28. Abelian group definition
  29. Coprime integers definition
  30. Empty set object
  31. Family of sets definition
  32. Ordered pair definition
  33. Group isomorphism definition
  34. Intersection definition
  35. Addition of natural numbers definition
  36. Union definition
  37. Commutative ring definition
  38. Polynomial ring definition
  39. Ring homomorphism definition
  40. Unit of a ring definition
  41. Zero divisor definition
  42. Left coset definition
  43. Right coset definition
  44. Set-builder notation concept
  45. The successor function is injective statement
  46. Zero is not a successor statement
  47. Biconditional definition
  48. Existential quantifier definition
  49. Universal quantifier definition
  50. Proof of the uniqueness of inverses proof
  51. Cartesian product definition
  52. Disjoint sets definition
  53. Order on the natural numbers definition
  54. Proof of the commutativity of addition by induction proof
  55. Group of units of a ring definition
  56. Divisibility in a commutative ring definition
  57. Subset definition
  58. Degree of a polynomial definition
  59. Polynomial evaluation definition
  60. Union of a family of sets definition
  61. Field definition
  62. Axiom of extensionality statement
  63. Integral domain definition
  64. Uniqueness quantifier definition
  65. Uniqueness of inverses statement
  66. Binary relation definition
  67. Commutativity of addition statement
  68. Partition of a set definition
  69. Leading coefficient definition
  70. Root of a polynomial definition
  71. Proof of cancellation in an integral domain proof
  72. Evaluation homomorphism definition
  73. Proof of strong induction from ordinary induction proof
  74. Finite field definition
  75. Reflexive relation definition
  76. Symmetric relation definition
  77. Transitive relation definition
  78. Proof of the laws of exponents in a group proof
  79. Monic polynomial definition
  80. Strong induction statement
  81. Multiplicity of a root definition
  82. Function definition
  83. Proof of the degree of a product over an integral domain proof
  84. Proof of the remainder theorem proof
  85. Cancellation in an integral domain statement
  86. Equivalence relation definition
  87. Laws of exponents in a group statement
  88. Proof of the well-ordering principle from strong induction proof
  89. Codomain definition
  90. Injective function definition
  91. Division algorithm for polynomials statement
  92. Degree of a product statement
  93. Order of an element definition
  94. Well-ordering principle statement
  95. Cyclic subgroup generated by an element definition
  96. Surjective function definition
  97. Remainder theorem statement
  98. Equivalence class definition
  99. Proof that R[x] is an integral domain iff R is proof
  100. Exponent of a group definition
  101. Proof of the division algorithm proof
  102. Cyclic group definition
  103. Bijective function definition
  104. Proof that equivalence classes form a partition proof
  105. Proof of the factor theorem proof
  106. R[x] is an integral domain iff R is statement
  107. Division algorithm statement
  108. Equinumerous sets definition
  109. Equivalence classes form a partition statement
  110. Factor theorem statement
  111. Cardinality definition
  112. Proof of Bézout's identity proof
  113. Proof that g to the n equals 1 iff the order divides n proof
  114. Proof that a polynomial over a field has at most as many roots as its degree proof
  115. g to the n equals 1 iff the order divides n statement
  116. Bézout's identity statement
  117. A polynomial over a field has at most as many roots as its degree statement
  118. Proof that cosets have the same cardinality as the subgroup proof
  119. Proof of the generalized Euclid's lemma proof
  120. Proof that the order of a cyclic subgroup equals the order of its generator proof
  121. Cosets have the same cardinality as the subgroup statement
  122. Generalized Euclid's lemma statement
  123. Order of a cyclic subgroup equals the order of its generator statement
  124. Proof of Lagrange's theorem proof
  125. Proof that a product of two finite cyclic groups is cyclic iff their orders are coprime proof
  126. Proof that cyclic groups of the same order are isomorphic proof
  127. Lagrange's theorem statement
  128. Proof that the order of an element divides the order of the group proof
  129. Cyclic groups of the same order are isomorphic statement
  130. Product of cyclic groups is cyclic iff the orders are coprime statement
  131. Order of an element divides the order of the group statement
  132. Proof that g to the order of the group is the identity proof
  133. Classification of finite abelian groups statement
  134. g to the order of the group is the identity statement
  135. Proof that a finite abelian group is cyclic iff its exponent equals its order proof
  136. A finite abelian group is cyclic iff its exponent equals its order statement
  137. Proof that finite subgroups of the multiplicative group of a field are cyclic proof
  138. Finite subgroups of the multiplicative group of a field are cyclic statement
  139. Proof that the multiplicative group of a finite field is cyclic proof

Where this leads

16 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Finite_field, Multiplicative structure
About this page
TagXXV5KB8CF0
URIm2://XXV5KB8CF0
Kindproof
WritingW0 stub
MSC12E20
ProvesThe multiplicative group of a finite field is cyclic
UsesFinite field, Group of units of a ring, Finite subgroups of the multiplicative group of a field are cyclic
Changed4 November 2026

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