\( \displaystyle \lim_{x \to \infty} \dfrac{\left(\sqrt{3x+1} + \sqrt{3x-1}\right)^{6} + \left(\sqrt{3x+1} - \sqrt{3x-1}\right)^{6}}{\left(x + \sqrt{x^{2} - 1}\right)^{6} + \left(x - \sqrt{x^{2} - 1}\right)^{6}} \, x^{3} \)
is equal to \( 27 \)
is equal to \( 9 \)
is equal to \( \dfrac{27}{2} \)
does not exist