(sinx+3)(sin4x2−sin2x2)+1=0⇔(sinx+3)sin2x2(sin2x2−1)+1=0⇔(sinx+3)sin2x2.cos2x2+1=0⇔(sinx+3)(2sinx2.cosx2)24+1=0⇔(sinx+3)sin2x4+1=0$\Leftrightarrow \sin^3 x +3 \sin^2 x +4 =0$
(sinx+3)(sin4x2−sin2x2)+1=0⇔(sinx+3)sin2x2(sin2x2−1)+1=0$\Leftrightarrow - (\sin x +3) \sin^2 \frac{x}{2}. \cos^2 \frac{x}{2} +1 =0$$\Leftrightarrow -(\sin x +3) \frac{(2 \sin \frac{x}{2}. \cos \frac{x}{2})^2}{4} +1 =0$$\Leftrightarrow -(\sin x +3) \frac{\sin^2 x}{4} +1 =0$$\Leftrightarrow -\sin^3 x -3 \sin^2 x +4 =0$