⇔√3/2.sinx+1/2.cosx=−cos3x⇔cos(x−π/3)=cos(3x−π)⇔x−π/3=3x−π+2kπ⇔x=π/3−kπhoặc $x-\pi/3=\pi-3x+\pi+2k\pi\Leftrightarrow x=7\pi/12+k\pi/2$
⇔√3/2.sinx+1/2.cosx=−cos3x⇔cos(x−π/3)=cos(3x−π)⇔x−π/3=3x−π+2kπ⇔x=π/3−kπhoặc $x-\pi/3=-3x+\pi+2k\pi\Leftrightarrow x=\pi/
3+k\pi/2$