3. Compute, by hand, the eigenvalues and eigenvectors of $\mathbf{A}$, and use them to solve $\mathbf {A x}=\mathbf {b} $ for $\mathbf{x}$ (use the "spectral method"). $$ \mathbf{A}=\left [\begin{array}{111} 1 & 1 & 0W & 1 & 0 & 1 0 & 1 & 1 \end{array} ight), \mathbf{b}=\left|\begin{array}{r} -1 11 3 \end{array} ight) $$ Spectral method: $$ \mathbf{x}=\frac{\left(\mathbf{u}_{1} \cdot \mathbf {b} ight)} {\lambda_{1}} \mathbf {u}_{1}+\frac{\left\mathbf {u}_{2} \cdot \mathbf {b} ight)}{\lambda_{2}} \mathbf{u}_{2}+\cdots+\frac{\left(\mathbf {u}_{n} \cdot \mathbf {b} ight)}{\lambda_{n}} \mathbf {u}_{n} $$CS. SD. 128