Se foloseste de trei ori formula sin 2a=2 sina·cosa (prima data a=4x, a doua oara a=2x si a treia oara a=x)
[tex]\dfrac{\sin8x}{8\sin x}=\dfrac{2\sin4x\cos4x}{8\sin x}=\dfrac{2\sin2x\cos2x\cos4x}{4\sin x}=[/tex]
[tex]=\dfrac{2\sin x\cos x\cos2x\cos4x}{2\sin x}=\cos x\cos2x\cos4x[/tex]
