Let $A=\left|\begin{array}{ccc}1 & 2 & -1 \\ \mid-2 & -1 & 1\end{array}\right|$ be the coefficient matrix of a homogeneous system in $\mathrm{x}, \mathrm{y}$, and $\mathrm{z}$. Solve this system to illustrate that a homogeneous system of 3 equations in the unknowns, $\mathrm{x}, \mathrm{y}, \mathrm{z}$ has a unique solution.