Найти sin a tg a gtg a если cos a =2/7

Найдем sin a, tg a, и ctg a. sin a = √(1 - (cos a)^2) = √(1 - (2/7)^2) = √(1 - 4/49) = √(45/49) = √45/7 tg a = sin a / cos a = (√45/7) / (2/7) = √45 / 2 ctg a = 1 / tg a = 1 / (√45 / 2) = 2 / √45.