Home sin 90 Proof of the reduction Formulas for angles (90°+α) or (π/2+α $ 18.99 4.6 (729) In stock Description Proof of the reduction Formulas for angles (90°+α) or (π/2+α)Proof of the reduction Formulas for angles (90°+α) or (π/2+α)Proof of the reduction Formulas for angles (90°+α) or (π/2+α)