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If $\alpha=\frac{\pi}{8}$, what is the value of $\cos \alpha \cos 2 \alpha \cos 4 \alpha$ ?
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As given : $\alpha=\frac{\pi}{8}$
$\cos \alpha \cos 2 \alpha \cos 4 \alpha=\cos \frac{\pi}{8} \cdot \cos \frac{\pi}{4} \cos \frac{\pi}{2}=0$
$\left(\because \cos \frac{\pi}{2}=0\right)$
$\cos \alpha \cos 2 \alpha \cos 4 \alpha=\cos \frac{\pi}{8} \cdot \cos \frac{\pi}{4} \cos \frac{\pi}{2}=0$
$\left(\because \cos \frac{\pi}{2}=0\right)$
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