(a) Find a simple asymptotic formula for \(\mathbb {P}(X>x)\), where \(X\) has the GAMMA\((\theta ,\alpha )\) density, \[ f(x)=\frac {1}{\theta ^{\alpha }\Gamma (\alpha )} x^{\alpha -1}e^{-x/\theta }, \qquad x>0. \]
(b) Let \(X_1,X_2,\ldots \) be i.i.d. GAMMA\((\theta ,\alpha )\). Find an increasing sequence \(a_n\) such that \(\limsup _{n\to \infty }X_n/a_n=1\) a.s., and prove it.