$1/\;\;\sin 10^\circ .\sin 50^\circ .\sin 70^\circ $
$2/\;\tan 9^\circ - \tan 27^\circ - \tan 63^\circ + \tan 81^\circ $
$3/\;{\kern 1pt} \sin \frac{\pi }{{16}}\cos \frac{\pi }{{16}}\cos \frac{\pi }{8}{\rm{ }}$
$4/\;\frac{{\tan 80^\circ }}{{\cot 25^\circ + \cot 75^\circ }} - \frac{{\cot 10^\circ }}{{\tan 25^\circ + \tan 75^\circ }}$
$5/\;{\kern 1pt} \frac{{4 + 7\sin 2x}}{5}\;{\kern 1pt} \;{\kern 1pt} \;{\kern 1pt} khi\;{\kern 1pt} \tan x = 0,2{\rm{ }}$
$6/\;{\kern 1pt} \tan \left( {\frac{\pi }{4} - 2x} \right)\;{\kern 1pt} \;{\kern 1pt} \;{\kern 1pt} khi\;{\kern 1pt} \;{\kern 1pt} \tan x = 2{\rm{ }}$
$7/\;{\kern 1pt} \;{\kern 1pt} \sin 2x\;{\kern 1pt} \;{\kern 1pt} \;{\kern 1pt} khi\;{\kern 1pt} \;{\kern 1pt} \cos x - \sin x\frac{1}{4}{\rm{ }}$
$8/\cos \frac{x}{2}\;{\kern 1pt} \;{\kern 1pt} khi\;{\kern 1pt} \sin x = \frac{{ - 12}}{{13}}\;{\kern 1pt} ;\;{\kern 1pt} \;{\kern 1pt} \pi < x < \frac{{3\pi }}{2}{\rm{ }}$
$9/\;{\kern 1pt} \sin \frac{a}{2}\;{\kern 1pt} \;{\kern 1pt} \;{\kern 1pt} khi\;{\kern 1pt} \;{\kern 1pt} \sin a = 0,8\;{\kern 1pt} ;0 < x < \frac{\pi }{2}{\rm{ }}$