9 A function f is defined for \(x > 0\) by \(\mathrm { f } ( x ) = \frac { 6 } { x ^ { 2 } + a }\), where \(a\) is a positive constant.
- Show that f is a decreasing function.
- Find, in terms of \(a\), the coordinates of the point of inflection on the curve \(y = \mathrm { f } ( x )\).