ΑC = 2·r·SIN(β) = 2·r·SIN(δ) (Th corda)
AC = 8 ; r = 5
SIN(β) = SIN(δ) = ΑC/(2·r) = 8/(2·5)= 4/5
β < pi/2
COS(β) = √(1 - SIN(β)^2)
COS(β) = √(1 - (4/5)^2)----> COS(β) = 3/5
δ > pi/2
COS(δ) = - √(1 - SIN(δ)^2)
COS(δ) = - √(1 - (4/5)^2)-----> COS(δ) = - 3/5