no goals
x : ℝ
h : cos x = 1
n : ℤ
hn : ↑n * π = x
hn0 : n % 2 = 0
⊢ ↑(n / 2) * (2 * π) = x
rwa [← mul_assoc, ← @Int.cast_two ℝ, ← Int.cast_mul,
  Int.ediv_mul_cancel ((Int.dvd_iff_emod_eq_zero _ _).2 hn0)]
x : ℝ
h : cos x = 1
n : ℤ
hn : ↑(n / 2) * (2 * π) + π = x
hn1 : n % 2 = 1
⊢ ↑(n / 2) * (2 * π) = x
x : ℝ
h : cos x = 1
n : ℤ
hn : ↑n * π = x
hn1 : n % 2 = 1
⊢ ↑(n / 2) * (2 * π) = x
rw [← Int.emod_add_ediv n 2, hn1, Int.cast_add, Int.cast_one, add_mul, one_mul, add_comm,
      mul_comm (2 : ℤ), Int.cast_mul, mul_assoc, Int.cast_two] at hn
x : ℝ
n : ℤ
h : -1 = 1
hn : ↑(n / 2) * (2 * π) + π = x
hn1 : n % 2 = 1
⊢ ↑(n / 2) * (2 * π) = x
x : ℝ
h : cos x = 1
n : ℤ
hn : ↑(n / 2) * (2 * π) + π = x
hn1 : n % 2 = 1
⊢ ↑(n / 2) * (2 * π) = x
rw [← hn, cos_int_mul_two_pi_add_pi] at h
no goals
x : ℝ
n : ℤ
h : -1 = 1
hn : ↑(n / 2) * (2 * π) + π = x
hn1 : n % 2 = 1
⊢ ↑(n / 2) * (2 * π) = x
exact absurd h (by norm_num)
no goals
x : ℝ
n : ℤ
h : -1 = 1
hn : ↑(n / 2) * (2 * π) + π = x
hn1 : n % 2 = 1
⊢ ¬-1 = 1
norm_num