pouvez-vous m'aiider svvvvp!!​

Réponse :

sin(2π/3) = sin(π/3) = √3/2

2sin(π/3)cos(π/3) = 2*(√3*2)*1/2 = √3/2

cos(2π/3) = - cos(π/3) = -1/2

2cos²(π/3) - 1 = 2(cos(2π/3) +1) /2) - 1 = cos(2π/3) + 1 - 1 = -cos(π/3) = -1/2

Tu fais la même chose pour la suite.