a. $\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ \\ f( x) =\frac{( 3-x)( x+1)}{x^{2} -4}\\ Quan\ sát\ BXD:\\ f( x) \leqslant 0\Leftrightarrow S=( -\infty ;-2) \cup [ -1;2) \cup [ 3;+\infty ) \end{array}$
b. $\displaystyle \begin{array}{{>{\displaystyle}l}} f( x) =\frac{\left( 9-x^{2}\right)( x-1)}{2-x}\\ Quan\ sát\ BXD:\\ f( x) \geqslant 0\Leftrightarrow S=( -\infty ;3] \cup [ 1;2) \cup [ 3;+\infty ) \end{array}$
