Using the method given in Eq. (2.5-25), find the joint probability density function \(p_{W Z}(w, z)\) when

\[ \begin{align*} & w=u^{2} \\ & z=u+v \tag{p.2-1} \end{align*} \]

and \(p_{U V}(u, v)=\operatorname{rect} u\) rect \(v\), where rect \(x=1\) for \(|x| \leq 1 / 2\) and is zero otherwise.