Réponse :
Explications étape par étape :
■ 91π/4 = 88π/4 + 3π/4 = 22π + 3π/4 --> 3π/4 .
cos(3π/4) = -√2 / 2
sin(3π/4) = √2 / 2
■ -13π/6 = -12π/6 - π/6 = -2π - π/6 --> -π/6 .
cos(-π/6) = √3 / 2
sin(-π/6) = -0,5 .
■ -81π/2 = -80π/2 - π/2 --> -π/2 .
sin(-π/2) = -1 .
■ 25π/3 = 24π/3 + π/3 --> π/3 .
cos(π/3) = 0,5
sin(π/3) = √(1-0,5²) = √0,75 = √3 / 2 ≈ 0,866 .
( on a utilisé cos²â + sin²â = 1 ♥ )
■ 45π/6 = 48π/6 - 3π/6 --> -π/2 .
sin(-π/2) = -1
cos(-π/2) = 0
