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@ChrisHughes24
Created November 17, 2020 22:31
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Proof of some problem in a tweet
import analysis.special_functions.trigonometric
open complex real
example (θ φ : ℝ) (h1 : θ ≤ pi) (h2 : -pi < θ)
(h3 : 0 < cos φ): arg (exp (I * θ) * cos φ) = θ :=
by rw [mul_comm, ← of_real_cos, arg_real_mul _ h3, mul_comm, exp_mul_I,
arg_cos_add_sin_mul_I h2 h1]
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