Найди значение функции y=cos(x+pi/3) при x=a, если: 1) a=pi/6 2) a=pi/3 3) a=pi/2, 4) a=7pi/6

 1) cos(π/6+π/3)=cosπ/2=0
 2)cos(π/3+π/3)=cos2π/3==-1/2
 3)cos(π/2+π/3)=-sinπ/3=-√3/2
  4)cos(7π/6+π/3)=cos9π/6=cos3π/2=0