$A= 2 \bigg ( \dfrac{\sqrt 3}{2} \sin 2x + \dfrac{1}{2}\cos 2x+\dfrac{\sqrt 3}{2} \sin x - \dfrac{1}{2}\cos x -1 \bigg )$
$=2\bigg ( \sin (2x-\dfrac{\pi}{6}) +\sin (x+\dfrac{\pi}{6} )-1\bigg )$
$=2 \bigg ( 2\sin \dfrac{3x}{2}.\cos \dfrac{\pi}{6} -1 \bigg )=2\sqrt 3 \sin \dfrac{3x}{2} -2$
còn lại quá dễ nhường bạn