SIN(β) = SIN(270° - α)
SIN(270° - α) = - COS(α)
COS(α) = √(1 - SIN(α)^2) = √(1 - (4/5)^2) = 3/5
SIN(β) = - 3/5
TAN(γ) = TAN(90° - α)= COT(α)
COT(α) = COS(α)/SIN(α)
COT(α) = 3/5/(4/5)---> COT(α) = 3/4
TAN(γ) = 3/4
COS(pi/2 - γ) = COS(pi/2)·COS(γ) + SIN(pi/2)·SIN(γ) = SIN(γ)
SIN(γ) = COS(α) = 3/5