Using the cosine of the sum of angles identity...
cos(x + π/3) = cos(x)⋅cos(π/3) - sin(x)⋅sin(π/3)
= cos(x)⋅(1/2) - sin(x)⋅(√3/2) (evaluate the cos(π/3) & sin(π/3) )
= (1/2)⋅[ cos(x) - sin(x)⋅(√3) ] (factor out 1/2)
= (1/2)⋅[ cos(x) - √3⋅sin(x) ] (move √3 to be
a coëfficient for
the sin(x) term)