\text { A function } \mathrm{f} \text { is defined for } x>0 \text { by } \mathrm{f}(x)=\frac{6}{x^{2}+a} \text {, where } a \text { is a positive constant. }

(a) Show that fis a decreasing function. ) Find, in terms of a, the coordinates of the point of inflection on the curve y = f(x).