Given the function
$$
f(x)=\frac{\theta}{x^2}, \quad x \geq \theta, \quad \theta>0,
$$
(a) Verify that it is a density function.
(b) Find the maximum likelihood estimators of $\theta$ and $1 / \theta$ for random samples of size $n$.
(c) Is the maximum likelihood estimator of $\theta$ unbiased?
(d) Find the method of moments estimators of $\theta$ and $1 / \theta$.