\[\left( x^{2} - 9 \right)\left( x^{2} - 5x + 6 \right) \leq 0\]
\[x^{2} - 5x + 6 =\]
\[= x^{2} - 3x - 2x + 6 =\]
\[= x(x - 3) - 2(x - 3) =\]
\[= (x - 3)(x - 2)\]
\[(x - 3)^{2}(x + 3)(x - 2) \leq 0\ \]
\[Ответ:\lbrack - 3;2\rbrack \cup \left\{ 3 \right\}.\]