Алгебра: Cos(пи/33) * cos(2*пи/33) * cos(4*пи/33) * cos(8*пи/33) * cos(16*пи/33)=?

Cos(пи/33) * cos(2пи/33) cos(4пи/33) cos(8пи/33) cos(16*пи/33)=?

Ответы

Ponny1 24.04.2021 21:30

$cos \frac{\pi }{33}\cdot cos\frac{2\pi}{33}\cdot cos\frac{4\pi}{33}\cdot cos\frac{8\pi }{33}\cdot cos\frac{16\pi }{33} =\\\\=\frac{1}{2sin\frac{\pi}{33}} \cdot \underbrace {2sin\frac{\pi }{33} cos\frac{\pi}{33}} \cdot cos\frac{2\pi }{33} \cdot cos\frac{4\pi }{33}\cdot cos \frac{8\pi}{33} \cdot cos\frac{16\pi}{33} =\\\\=\frac{1}{2sin\frac{\pi}{33}}\cdot \underbrace {sin\frac{2\pi}{33}\cdot cos\frac{2\pi}{33}}\cdot cos\frac{4\pi}{33}\cdot cos\frac{8\pi}{33} \cdot cos\frac{16\pi }{33}=$

$=\frac{1}{2sin\frac{\pi}{33}}\cdot \frac{1}{2}\underbrace {sin\frac{4\pi}{33}\cdot cos\frac{4\pi}{33}}\cdot cos\frac{8\pi}{33}\cdot cos\frac{16\pi}{33}=\\\\= \frac{1}{2sin\frac{\pi}{33}} \cdot \frac{1}{2}\cdot \frac{1}{2}\underbrace {sin\frac{8\pi}{33}\cdot cos\frac{8\pi}{33} }\cdot cos\frac{16\pi}{33} =\\\\= \frac{1}{2sin\frac{\pi}{33}} \cdot \frac{1}{4}\cdot \frac{1}{2}\underbrace {sin\frac{16\pi}{33}\cdot cos\frac{16\pi}{33}}=$

$= \frac{1}{2sin\frac{\pi}{33}} \cdot \frac{1}{8} \cdot \frac{1}{2} \cdot sin\frac{32\pi}{33}=$

$= \frac{1}{2sin\frac{\pi}{33}} \cdot \frac{1}{16}\cdot sin(\pi -\frac{\pi}{33}) =\frac{1}{32sin\frac{\pi}{33}}\cdot sin\frac{\pi}{33}=\frac{1}{32}$