If \( \tan\left( \dfrac{\pi}{9} \right), x, \tan\left( \dfrac{7\pi}{18} \right) \) are in arithmetic progression and \( \tan\left( \dfrac{\pi}{9} \right), y, \tan\left( \dfrac{5\pi}{18} \right) \) are also in arithmetic progression, then \( |x - 2y| \) is equal to:
