Questions in trigonometry

Select	Question
	$\cos \frac{2\pi }{15}\cos \frac{4\pi }{15}\cos \frac{8\pi }{15}\cos \frac{16\pi }{15}$ =
	The value of ${{\cos }^{2}}\frac{\pi }{12}+{{\cos }^{2}}\frac{\pi }{4}+{{\cos }^{2}}\frac{5\pi }{12}$ is
	The value of $\sin \frac{\pi }{16}\sin \frac{3\pi }{16}\sin \frac{5\pi }{16}\sin \frac{7\pi }{16}$is
	${{\cos }^{2}}{{76}^{o}}+{{\cos }^{2}}{{16}^{o}}-\cos {{76}^{o}}\cos {{16}^{o}}=$
	$\cos \frac{\pi }{7}\cos \frac{2\pi }{7}\cos \frac{4\pi }{7}=$
	The value of $\frac{\tan {{70}^{o}}-\tan {{20}^{o}}}{\tan {{50}^{o}}}=$
	${{\cos }^{2}}\alpha +{{\cos }^{2}}(\alpha +120{}^\circ )+{{\cos }^{2}}(\alpha -120{}^\circ )$ is equal to
	The value of $\tan {{20}^{o}}+2\tan {{50}^{o}}-\tan {{70}^{o}}$is equal to
	$\frac{{{\cot }^{2}}15{}^\circ -1}{{{\cot }^{2}}15{}^\circ +1}=$
	If $\cos \theta =\frac{3}{5}$and $\cos \varphi =\frac{4}{5},$where $\theta $and $\varphi $are positive acute angles, then $\cos \frac{\theta -\varphi }{2}=$