1)cos 3 x cos x - sin 3x sin x
2)tg 20П/3
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