[latex] \frac{2tg( \frac{\pi }{6}) }{tg ^{2}( \frac{ \pi }{6}) - 1 } [/latex]

[latex] \frac{2tg\frac{pi}{6}}{tg^2\frac{\pi}{6}-1}= - \frac{2tg\frac{\pi}{6}}{1-tg^2\frac{\pi}{6}} =-tg\frac{\pi}{3}=-\sqrt3[/latex]