Question

1)cos 3 x cos x - sin 3x sin x

 

2)tg 20П/3

Answer 1

cos3x * cosx - sin3x * sinx=cos(3x-x)=cos2x

tg20π/3=tg(18π+2π)/3=tg(6π+2π/3)=tg2π/3=tg(π-π/3)=tg(-π/3)= -tgπ/3= -√3

  или сразу   tg20π/3=tg(7π-π/3)= tg(-π/3)=-tgπ/3=-√3