Question

упростите выражение
cos^2t + ctg^2t cos^2t - ctg^2t

Answer 1

cos²t + ctg²t · cos²t - cos²t / sin²t =
= cos²t (1 + ctg²t - 1/sin²t) = cos²t (1/sin²t - 1/sin²t) = 0

Использовалось тождество:
1 + ctg²t = 1 / sin²t