a) 13π 13π COS =cos- 4 4 b) Ta có: Π = cos(3x+4)= cos(x+4)--cos√ A=sin(-a)+cos (플-a)+ 3п -a+tan α-cot α 2 =-sin α+ sin α+tan α- cot π- =-sin α+ sin α + tan α-cot 2 -α-sin a+sinα+tan α-tan α = 0. (플-a)=-