case h
x✝ : ℝ
⊢ cos (↑x✝ - ↑(π / 2)) = sin ↑x✝
θ : Angle
⊢ cos (θ - ↑(π / 2)) = sin θ
induction θ using Real.Angle.induction_on
no goals
case h
x✝ : ℝ
⊢ cos (↑x✝ - ↑(π / 2)) = sin ↑x✝
exact Real.cos_sub_pi_div_two _