`x(x + 5) <= 2(x^2 + 2)`
`-> x^2 + 5x <= 2x^2 + 4`
`-> x^2 - 5x + 4 <= 0`
`-> (x - 4)(x - 1) <= 0`
`->` \(\left[ \begin{array}{l}\left\{ \begin{array}{l}x - 4 ≤ 0\\x - 1 \≥ 0\end{array} \right.\\\left\{ \begin{array}{l}x - 4 ≥ 0\\x - 1 ≤ 0\end{array} \right.\end{array} \right.\)
`-> -1 <= x <= 4`
