Tg A = BC/AC => AC = BC/tg A
sqrt - корень
cos A = 1 - sin A = 1 - sqrt(5)/5 = (5-sqrt(5))/5
Tg A = sqrt(5)/5 * 5/(5-sqrt(5)) = sqrt(5)/(5-sqrt(5))
AC = 5 * (5-sqrt(5))/sqrt(5))
