case h
ψ x✝ : ℝ
⊢ cos ↑x✝ = Real.cos ψ ↔ ↑x✝ = ↑ψ ∨ ↑x✝ = -↑ψ
θ : Angle
ψ : ℝ
⊢ cos θ = Real.cos ψ ↔ θ = ↑ψ ∨ θ = -↑ψ
induction θ using Real.Angle.induction_on
no goals
case h
ψ x✝ : ℝ
⊢ cos ↑x✝ = Real.cos ψ ↔ ↑x✝ = ↑ψ ∨ ↑x✝ = -↑ψ
exact cos_eq_iff_coe_eq_or_eq_neg