CX=b
==> X = C^(-1) * b
=\( \left(\begin{array}{ll}1 & 2 \\ 3 & 4\end{array}\right)^{-1} \cdot \left(\begin{array}{c}1 \\ -1\end{array}\right) \)
=\( \left(\begin{array}{ll}-2 & 1 \\ 1,5 & -0,5\end{array}\right)^{-1} \cdot \left(\begin{array}{c}1 \\ -1\end{array}\right) \)
=\( \left(\begin{array}{c}-3 \\ 2\end{array}\right) \)