matrix invers
for 2x2
\[ A^{-1} = \frac{1}{(a \cdot d) - (b \cdot c)} \begin{bmatrix} d & -b & \newline -c & a \end{bmatrix}\]
for 3x3 \[ A^{-1} = \frac{1}{\det A} \text{adj } A \]
for 2x2
\[ A^{-1} = \frac{1}{(a \cdot d) - (b \cdot c)} \begin{bmatrix} d & -b & \newline -c & a \end{bmatrix}\]
for 3x3 \[ A^{-1} = \frac{1}{\det A} \text{adj } A \]