Q. I. The pdf of the population X is f(x) =
$$\begin{cases}
\lambda^2xe^{-\lambda x}, & x > 0 \\
0, & others
\end{cases}$$
The parameter λ (λ > 0) is unknown, X1, X2, ..., Xn is random sample
from the population X.
(1) What is the moment estimator of λ;
(2) What the MLE estimator of λ.