Invertible Matrix

A matrix, which when multiplied by another matrix, results in the identity matrix.

\begin{equation} \mathbf{A}\mathbf{A}^{-1} = I \end{equation}

e.g.

\begin{equation} \begin{bmatrix} a & b\\\
c & d \end{bmatrix} \begin{bmatrix} d & -b\\\
-c & a \end{bmatrix}= \begin{bmatrix} 1 & 0\\\
0 & 1 \end{bmatrix} \end{equation}