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