`x in (-infty; -2] cup [2; +infty)`
`3sqrt{x + 2} - sqrt{x^2 - 4} = 0`
`-> 3sqrt{x + 2} - sqrt{x - 2}.sqrt{x + 2} = 0`
`-> sqrt{x + 2}(3 - sqrt{x - 2}) = 0`
`->` \(\left[ \begin{array}{l}x + 2 = 0\\3 = \sqrt{x - 2}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x = -2\ (nhận)\\9 = x - 2\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x = -2\\x = 11\ (nhận)\end{array} \right.\)
`-> S = {-2; 11}`
