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$\cos\, \frac{\pi}{6}=\frac{1}{2}$

$\sin\, \frac{\pi}{3}=\frac{1}{2}$

$\sin(-a)=-\sin a$

$\mbox{tg }\, \frac{\pi}{6}=\frac{\sqrt{3}}{3}$

$\sin^2{a}=1+\cos^2{a}$

$\cos{(\pi-a)}=\sin{a}$

$\cos\, \frac{\pi}{4}=\frac{1}{2}$

$\mbox{tg }\frac{\pi}{2}=0$

$\cos{(a+b)}=\cos{a}\cos{b}+\sin{a}\sin{b}$

$\mbox{tg }(-a)=\mbox{tg }a$