9 A curve has equation
$$y = \frac { 4 x - 3 a } { 2 \left( x ^ { 2 } + a ^ { 2 } \right) }$$
where \(a\) is a positive constant.
- Explain why the curve has no asymptotes parallel to the \(y\)-axis.
- Find, in terms of \(a\), the set of values of \(y\) for which there are no points on the curve.
- Find the exact value of \(\int _ { a } ^ { 2 a } \frac { 4 x - 3 a } { 2 \left( x ^ { 2 } + a ^ { 2 } \right) } \mathrm { d } x\), showing that it is independent of \(a\).