Geometry
# Proving Trigonometric Identities

$\large \dfrac1{2^x} = \cos (a) \cos(2a) \cos(3a) \cdots \cos(999a)$

The equation above holds true for $a = \dfrac{2\pi}{1999}$. Find $x$.

$\large \tan\frac{\pi}{7}\tan\frac{2\pi}{7}\tan\frac{3\pi}{7}= \sqrt{A}$ Find $A$.

$\large f(x) = \cos(x) \cdot \cos(2x) \cdot \cos(3x)\cdots \cos(999x)$

If $f \left(\dfrac{2\pi }{1999}\right) = \dfrac{1}{2^{k}}$, find $k$.