Вычислить tg 15 градусов

Tg15=tg (45-30) = (tg45-tg30) / (1+tg45*tg30) = (1-√3/3) / (1+1*√3/3) =

= ((3-√3) / 3) / ((3+√3) / 3) = (3-√3) (3+√3) = (3-√3) ² / (3² - (√3) ²) = (9-6√3+3) / (9-3) =

= (12-6√3) / 6=2-3√3