I am attempting to learn how to find a complete and sufficient statistic. So, I am working on this problem for class:
Let $X_1, \cdot\cdot\cdot,X_n$ be a random sample from the pdf $f(x_i|u)=e^{-(x-\mu)}$, where $- \infty < \mu < x_i <\infty$. Show that $X_{1} = min_i\{X_i\}$ is a complete sufficient statistic.
Here is what I have done so far. First I tried to show it is sufficient by factorization theorem:
$\prod_{i=1}^{n} f(x_1,...,x_n|\theta) = exp^{-\sum_{i=1}^{n}x_i+n\mu} I\{\mu<x_{(1)}<\infty\}$.
$g(T(X|\theta)=exp^{-\sum_{i=1}^{n}x_i+n\mu}$
$h(X) = 1$.
First why is $min_i\{X_i\}$ a sufficient in this case? I know that for a statistic to be complete it must also satisfy the condition that for all $g(.)$ the expectation of $E[g(T)]=0$. and this should happen with probability 1. So then I must take the expectation of a function of T to show the completeness, but I am not sure if how I proceeded is correct. Thanks in advance!