MathNet 2021 — Part 01 Question 38

Question 38

Let $c = \frac{2\pi}{11}$. What is the value of
$$
\frac{\sin 3c \cdot \sin 6c \cdot \sin 9c \cdot \sin 12c \cdot \sin 15c}{\sin c \cdot \sin 2c \cdot \sin 3c \cdot \sin 4c \cdot \sin 5c} ?
$$

$-1$
$-\frac{\sqrt{11}}{5}$
$\frac{\sqrt{11}}{5}$
$\frac{10}{11}$
$1$