Two vectors \( \vec{X} \) and \( \vec{Y} \) have equal magnitude. The magnitude of \( (\vec{X}-\vec{Y}) \) is \( n \) times the magnitude of \( (\vec{X}+\vec{Y}) \). The angle between \( \vec{X} \) and \( \vec{Y} \) is:
\( \cos^{-1}\!\left(\frac{n^{2}+1}{-n^{2}-1}\right) \)
\( \cos^{-1}\!\left(\frac{-n^{2}-1}{n^{2}-1}\right) \)
\( \cos^{-1}\!\left(\frac{n^{2}+1}{n^{2}-1}\right) \)
\( \cos^{-1}\!\left(\frac{n^{2}-1}{n^{2}+1}\right) \)