$($c$)(6$ Points$)$ Find the singular configurations of this manipulator. For each singularity$,$ draw the

robot configuration and clearly state how the movement is restricted $($in terms of frame axes$).$

Hint: The linear Jacobian in frame $\{2\}$ is given to you here:

${?}^2{J}_v=\left[\begin{array}{ccc}-L_1{s}_2& 0& -L_3{s}_3\\ L_1{c}_2+L_2+L_3{c}_3& L_2+L_3{c}_3& 0\\ 0& 0& -L_3{c}_3\end{array}\right]$