Complex roots of unity

In this file we show that the n-th complex roots of unity are exactly the complex numbers exp (2 * π * I * (i / n)) for i ∈ Finset.range n.

Main declarations

• Complex.mem_rootsOfUnity: the complex n-th roots of unity are exactly the complex numbers of the form exp (2 * π * I * (i / n)) for some i < n.
• Complex.card_rootsOfUnity: the number of n-th roots of unity is exactly n.

theorem Complex.isPrimitiveRoot_exp_of_coprime (i : ℕ) (n : ℕ) (h0 : n ≠ 0) (hi : Nat.Coprime i n) : IsPrimitiveRoot (Complex.exp (2 * ↑Real.pi * Complex.I * (↑i / ↑n))) n

theorem Complex.isPrimitiveRoot_exp (n : ℕ) (h0 : n ≠ 0) : IsPrimitiveRoot (Complex.exp (2 * ↑Real.pi * Complex.I / ↑n)) n

theorem Complex.isPrimitiveRoot_iff (ζ : ℂ) (n : ℕ) (hn : n ≠ 0) : IsPrimitiveRoot ζ n ↔ ∃ i, i < n ∧ ∃ x, Complex.exp (2 * ↑Real.pi * Complex.I * (↑i / ↑n)) = ζ

theorem Complex.mem_rootsOfUnity (n : ℕ+) (x : ℂˣ) : x ∈ rootsOfUnity n ℂ ↔ ∃ i, i < ↑n ∧ Complex.exp (2 * ↑Real.pi * Complex.I * (↑i / ↑↑n)) = ↑x

The complex n-th roots of unity are exactly the complex numbers of the form exp (2 * Real.pi * Complex.I * (i / n)) for some i < n.

theorem Complex.card_rootsOfUnity (n : ℕ+) : Fintype.card { x // x ∈ rootsOfUnity n ℂ } = ↑n

theorem Complex.card_primitiveRoots (k : ℕ) : Finset.card (primitiveRoots k ℂ) = Nat.totient k

theorem IsPrimitiveRoot.norm'_eq_one {ζ : ℂ} {n : ℕ} (h : IsPrimitiveRoot ζ n) (hn : n ≠ 0) : ‖ζ‖ = 1

theorem IsPrimitiveRoot.nnnorm_eq_one {ζ : ℂ} {n : ℕ} (h : IsPrimitiveRoot ζ n) (hn : n ≠ 0) : ‖ζ‖₊ = 1

theorem IsPrimitiveRoot.arg_ext {n : ℕ} {m : ℕ} {ζ : ℂ} {μ : ℂ} (hζ : IsPrimitiveRoot ζ n) (hμ : IsPrimitiveRoot μ m) (hn : n ≠ 0) (hm : m ≠ 0) (h : Complex.arg ζ = Complex.arg μ) : ζ = μ

theorem IsPrimitiveRoot.arg_eq_zero_iff {n : ℕ} {ζ : ℂ} (hζ : IsPrimitiveRoot ζ n) (hn : n ≠ 0) : Complex.arg ζ = 0 ↔ ζ = 1

theorem IsPrimitiveRoot.arg_eq_pi_iff {n : ℕ} {ζ : ℂ} (hζ : IsPrimitiveRoot ζ n) (hn : n ≠ 0) : Complex.arg ζ = Real.pi ↔ ζ = -1

theorem IsPrimitiveRoot.arg {n : ℕ} {ζ : ℂ} (h : IsPrimitiveRoot ζ n) (hn : n ≠ 0) : ∃ i, Complex.arg ζ = ↑i / ↑n * (2 * Real.pi) ∧ IsCoprime i ↑n ∧ Int.natAbs i < n