Упростите:
cosa+cos(2п/3 + a) + cos(2п/3 - a)

на фото

* * * cos(α + β) = cosαcosβ - sinαsinβ ;

cos(α - β) = cosαcosβ + sinαsinβ ; cos(2π/3) = - 1/2 * * *

cosα + cos(2π/3 + α) + cos(2π/3 - α) =

= cosα + cos(2π/3)cosα - sin(2π/3)sinα + cos(2π/3)cosα + sin(2π/3)sinα =

= cos + cos(2π/3)cosα + cos(2π/3)cosα = cosα - 1/2 · cosα - 1/2 · cosα =

= 1/2 · cosα - 1/2 · cosα = 0