Ответ:

  1. а) tg(π/4) + ctg(5π/4) = 1 + 1 = 2.
  2. б) ctg(π/3) · tg(π/6) = (√3/3) · (√3/3) = 1/3.
  3. в) tg(π/6) − ctg(π/6) = √3/3 − √3 = −2√3/3.
  4. г) По периодичности tg(9π/4) = tg(π/4) = 1, а ctg(π/4) = 1. Сумма равна 2.