θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ 2 • θ = ↑π ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
θ : Angle
⊢ 2 • θ = ↑π ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
have h : (π : Angle) = (2 : ℕ) • (π / 2 : ℝ) := by rw [two_nsmul, add_halves]
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ 2 • θ = ↑(2 • (π / 2)) ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ 2 • θ = ↑π ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
nth_rw 1 [h]
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ θ = ↑(π / 2) ∨ θ = ↑(π / 2) + ↑π ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ 2 • θ = ↑(2 • (π / 2)) ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
rw [coe_nsmul, two_nsmul_eq_iff]
case h.e'_2.h.e'_2.h.e'_3
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ ↑(-π / 2) = ↑(π / 2) + ↑π
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ θ = ↑(π / 2) ∨ θ = ↑(π / 2) + ↑π ↔ θ = ↑(π / 2) ∨ θ = ↑(-π / 2)
convert Iff.rfl
no goals
case h.e'_2.h.e'_2.h.e'_3
θ : Angle
h : ↑π = ↑(2 • (π / 2))
⊢ ↑(-π / 2) = ↑(π / 2) + ↑π
rw [add_comm, ← coe_add, ← sub_eq_zero, ← coe_sub, neg_div, ←neg_sub, sub_neg_eq_add, add_assoc,
  add_halves, ← two_mul, coe_neg, coe_two_pi, neg_zero]
no goals
θ : Angle
⊢ ↑π = ↑(2 • (π / 2))
rw [two_nsmul, add_halves]