[tex]\boxed{\begin{array}{l}\begin{cases}\sf 9x-y=3\\\sf x+2y=9\end{cases}\\\\\begin{bmatrix}\sf9&\sf-1\\\sf1&\sf2\end{bmatrix}\cdot\begin{bmatrix}\sf x\\\sf y\end{bmatrix}=\begin{bmatrix}\sf3\\\sf9\end{bmatrix}\\\sf D=9\cdot2-(-1)\cdot1=18+1=19\\\begin{bmatrix}\sf3&\sf-1\\\sf9&\sf2\end{bmatrix}\\\sf D_x=3\cdot2-(-1)\cdot9=6+9=15\\\begin{bmatrix}\sf9&\sf3\\\sf1&\sf9\end{bmatrix}\\\sf D_y=9\cdot9-3\cdot1=81-3=78\end{array}}[/tex]
