\(1+\sin\dfrac{x}{2}\sin x-\cos\dfrac{x}{2}\sin^2x=2\cos^2\left(\dfrac{\Pi}{4}-\dfrac{x}{2}\right)\)
\(\Leftrightarrow1+\sin\dfrac{x}{2}\sin x-\cos\dfrac{x}{2}\sin^2x=2\left(\dfrac{\sqrt{2}}{2}\cos\dfrac{x}{2}+\dfrac{\sqrt{2}}{2}\sin\dfrac{x}{2}\right)^2\)
\(\Leftrightarrow1+2\sin^2\dfrac{x}{2}\cos\dfrac{x}{2}-\cos\dfrac{x}{2}\left(2\sin\dfrac{x}{2}\cos\dfrac{x}{2}\right)^2=1+2\sin\dfrac{x}{2}\cos\dfrac{x}{2}\)
\(\Leftrightarrow2\sin^2\dfrac{x}{2}\cos\dfrac{x}{2}-4\cos^3\dfrac{x}{2}\sin^2\dfrac{x}{2}-2\sin\dfrac{x}{2}\cos\dfrac{x}{2}=0\)
\(\Leftrightarrow2\sin\dfrac{x}{2}\cos\dfrac{x}{2}\left(\sin\dfrac{x}{2}-2\sin\dfrac{x}{2}\cos^2\dfrac{x}{2}-1\right)=0\)
\(\Leftrightarrow2\sin\dfrac{x}{2}\cos\dfrac{x}{2}\left(\sin\dfrac{x}{2}-2\sin\dfrac{x}{2}\left(1-\sin^2\dfrac{x}{2}\right)-1\right)=0\)
\(\Leftrightarrow2\sin\dfrac{x}{2}\cos\dfrac{x}{2}.\left(\sin\dfrac{x}{2}-1\right)\left(2\sin^2\dfrac{x}{2}+2\sin\dfrac{x}{2}+1\right)=0\)
