[Cos(x-π/4) =sin (3x+π/3)…………….A
SIN(x) =cos (π/2-x) : نعلم أن
Sin (3x+π/3) =cos [π/2-(3x+π/3)]
=cos (π/6-3x)
Cos(x-π/4) =cos (π/6-3x) : A نجد بالتعويض في المعادلة
X-π/4= (π/6-3x) +2πk
(X-π/4)=-(π/6-3x) +2πk k/z
4x=5π/12+2πk
-2x=π/12+2πk
S= {5π/48+2πk/4;-π/4-2πk/2b