1) tqx = - 1/√3 ;
x = - π/6 +π*k .k∈Z.
2) cos2x = -√3/2 ;
2x = (±)(π-π/6) +2π*k ;
x =±5π/12 +π*k ,k∈Z .
3) sin(x/3+π/2) = -1/2;
cosx/3 = -1/2 ;
x/3 = (±)(π-π/3)+2π*k ;
x= ±2π +6π*k , k∈Z.
4) cos²x +2cosx -3 =0 ;
замена t =cosx ; -1 ≤ t ≤1.
t² + 2t -3 =0 (квадратное уравнение) ;
t₁= - 3 _ не решение ;
t₂= 1.
cosx =1 ;
x =2π*k ,k∈Z .