a) $(x -1)(2x -3)>0$
$\to \left[\begin{array}{l}\begin{cases}x -1 > 0\\2x - 3 > 0\end{cases}\\\begin{cases}x - 1 < 0\\2x - 3 < 0\end{cases}\end{array}\right.$
$\to \left[\begin{array}{l}x >\dfrac32\\x < 1\end{array}\right.$
b) $(x^2 +2)(x -5)> 0$
$\to x -5 > 0\qquad (Do\,\, x^2 + 2 > 0\,\,\forall x)$
$\to x > 5$