Let \(\left(\mathbf{X}_{0}, \mathbf{U}_{0}\right)\) be an arbitrary point in
\(\mathbb{R}^{n+m}\). Give an example of a function \(\mathbf{F}\) :
\(\mathbb{R}^{n+m} \rightarrow \mathbb{R}^{m}\) such that \(\mathbf{F}\) is
continuously differentiable on \(\mathbb{R}^{n+m},
\mathbf{F}\left(\mathbf{X}_{0}, \mathbf{U}_{0}\right)=0\),
\(\mathbf{F}_{\mathbf{u}}\left(\mathbf{X}_{0}, \mathbf{U}_{0}\right)\) is
singular, and the conditions \(\mathbf{F}(\mathbf{X}, \mathbf{U})=\mathbf{0}\)
and \(\mathbf{U}\left(\mathbf{X}_{0}\right)=\mathbf{Y}_{\mathbf{0}}\)
(a) determine \(\mathbf{U}\) as a continuously differentiable function of
\(\mathbf{X}\) for all \(\mathbf{X}\);
(b) determine \(\mathbf{U}\) as a continuous function of \(\mathbf{X}\) for all
\(\mathbf{X}\), but \(\mathbf{U}\) is not differentiable at \(\mathbf{X}_{0}\)
(c) do not determine \(\mathbf{U}\) as a function of \(\mathbf{X}\).