1/3(cos4x*cos7x+sin2x)+1/3*sin4x*sin7x

Question

1/3(cos4x*cos7x+sin2x)+1/3*sin4x*sin7x

Answer 1

1/3(cos4xcos7x+sin4xsin7x)+1/3sin2x=1/3cos(7x-4x)+1/3sin2x=1/3cos3x+1/3sin2x=
1/3(sin2x+cos3x)=1/3(sin2x+sin(π/2-3x))=1/3*2sin(π/4-x/2)cos(5x/2-π/4)=
2/3sin(π/4-x/2)cos(5x/2-π/4)