# Let's salute cos 2

$\left(1+\cos \dfrac{\pi}{10}\right) \left(1+\cos \dfrac{3\pi}{10}\right) \left(1+\cos \dfrac{7\pi}{10}\right) \left(1+\cos \dfrac{9\pi}{10}\right)$

Find the reciprocal of the value of the expression above.

×