Докажите тождество - ctg (-a) - sin (-a) / 1+cos (-a) = 1/sin a

(sin a) / (1-cos a) - (1+cos a) / (sin a) = 0 ((sin^2 a) - (1-cos a) * (1+cos a)) / ((1-cos a) * (sin a)) = 0 ((sin^2 a) - 1 + (cos^2 a)) / ((1-cos a) * (sin a)) = 0 (1-1) / ((1-cos a) * (sin a)) = 0 0 / ((1-cos a) * (sin a)) = 0 0=0, доказано.