16 sin $\left(20°\right)$ sin$\left(40°\right)$ sin$\left(80°\right)$ is equal to :

16 sin20^o sin 40^o sin 80^o

$$\begin{gathered} =16\sin 40°\sin 20°\sin 80° \\ =4\left(4\sin \right(60-20\left)\sin \right(20\left)\sin \right(60+20\left)\right) \\ =4\times \sin \left(3\times 20°\right) \\ [\because \sin 3\theta =4\sin (60-\theta )\times \sin \theta \times \sin (60+\theta \left)\right] \\ =4\times \sin 60° \\ =4\times \frac{\sqrt{3}}{2}=2\sqrt{3} \end{gathered}$$