\(=1+\sin x-\sin7x-\cos5x-2\cdot\dfrac{1+\cos3x}{2}\)
\(=1+\sin\left(\dfrac{x-7x}{2}\right)\cdot\cos\left(\dfrac{x+7x}{2}\right)-\cos5x-1-\cos3x\)
\(=\sin\left(-3x\right)\cdot\cos4x-\left(\cos5x+\cos3x\right)\)
\(=-\sin3x\cdot\cos4x-2\left[\cos4x\cdot\cos x\right]\)
\(=-\cos4x\left(\sin3x+2\cos x\right)\)