Để \(A\cap B\ne\varnothing\)
\(\Leftrightarrow9a>\frac{4}{a}\)
\(\Leftrightarrow9a-\frac{4}{a}>0\)
\(\Leftrightarrow\frac{9a^2-4}{a}>0\)
\(\Leftrightarrow\frac{\left(3a-2\right)\left(3a+2\right)}{a}>0\)
\(\Rightarrow\left[{}\begin{matrix}a>\frac{3}{2}\\-\frac{3}{2}< a< 0\end{matrix}\right.\)