$tg frac{20 pi }{3} =$
$tg frac{28 pi }{3} =$
$tg(- frac{31 pi }{6} )=$
$ctg frac{16 pi }{3}$

Tg $frac{20*pi}{3}$ =tg(7π- $frac{pi}{3}$ ) =-tg $frac{pi}{3}$ =-√3

tg $frac{28*pi}{3}$ =tg(9π+ $frac{pi}{3}$ ) =tg $frac{pi}{3}$ =√3

tg(- $frac{31*pi}{6}$ )=-tg $frac{31*pi}{6}$ =-tg(5π+ $frac{pi}{6}$ )=-tg $frac{pi}{6}$ =- $frac{1}{ sqrt{3} }$

ctg $frac{16*pi}{3}$ =ctg(5π+ $frac{pi}{3}$ )=ctg $frac{pi}{3}$ = $frac{1}{ sqrt{3} }$