Question

Вычислить:
(cos 75 град - sin 75 град) в квадрате


tg п/8 делить на 1-tg^2 п/8

Answer 1

1)  (cos75° - sin75°)² = cos²75° - 2sin75°cos75° + cos²75° = 1 - 2sin(2*75°) =
= 1 - 2sin(180° - 30°) 1 - 2*sin30° = 1 - 2*(1/2) = 1 - 1 = 0
2)  tg(п/8) / (1 - tg²(п/8)) = (1/2)* [2 tg(п/8) / (1 - tg²(п/8))] = (1/2)*tg2*(π/8)) =
= (1/2)*tg(π/4) = (1/2)*1 = 1/2