+ = − +X X X X X2(COS 3 SIN ).COS COS 3 SIN 1⇔ − + = −2X X X X...

Câu 2. + = − +x x x x x2(cos 3 sin ).cos cos 3 sin 1⇔ − + = −

2

(2 cos 1) 2 3 sin cos cos 3 sin⇔ + = −x x x xcos 2 3 sin 2 cos 3 sin1 3 1 3cos 2 sin 2 cos sin2 2 2 2π πx xsin(2 ) sin( )6 6π π π + = − +  =x x k x k2 2 2π 6 6 3⇔ ⇔ ∈Z)5 2 (k + = + +  = + 