Given $f(x)$ continuous for all $x\in \mathbb R$, and $f(x)$ nonzero on $\mathbb R$, $0 such that $|f(x)|\leq e^{a|x|}$ for all $x\in \mathbb R$. What conditions should $f$ have so that the integral
$\int_{-\infty}^{\infty}\bigg|\frac{e^{b|x|}}{f(x)}\bigg|^{2}\,dx$ be finite?