Solution
= Solution
Let $M=X_{(n)}=\max_iX_i$. The <likelihood function> is
$$
L(\theta;x_1,\ldots,x_n)
=(2\theta)^{-n}\mathbf1_{\{M\le2\theta\}}.
$$
On its feasible range $\theta\ge M/2$, this is decreasing in $\theta$. Therefore the <maximum likelihood estimation>[maximum likelihood estimator] is
$$
\boxed{\widehat\theta=\frac M2}.
$$