Найдите sin A, если: а) ctg A = 2; б) ctg A = 1/3

ctg(a) = cos(a)/sin(a) cos(a)/sin(a) = - 2 cos(a) = - 2sin(a) cos²(a) + sin²(a) = 1 (-2sin(a))² + sin²(a) = 1 4sin²(a) + sin²(a) = 1 sin²(a) = 1/5 sin(a) = √1/5