cos (x + y) = cos x cos y - sin x sin y, color(crimson)("basic trigonometric identity"cos(x+y)=cosxcosy−sinxsiny,basic trigonometric identity
4 cos (x + (pi/3))4cos(x+(π3))
=> 4 (cosx cos (pi/3) - sinx sin (pi/3))⇒4(cosxcos(π3)−sinxsin(π3))
=> 4 * (cos x/2 - (sqrt3 sin x) / 2), color(crimson)(" as " cos (pi/3) = 1/2, sin (pi/3) = sqrt3/2⇒4⋅(cosx2−√3sinx2), as cos(π3)=12,sin(π3)=√32
color(indigo)(=> 2 (cos x - sqrt3 sin x)⇒2(cosx−√3sinx)