## College Algebra (6th Edition)

$\left[\begin{array}{ll} 1 & 0\\ 0 & 1 \end{array}\right]$
The multiplicative identity matrix $I_{n}$ is an $n\times n$ matrix with 1s down the main diagonal from upper left to lower right and 0s elsewhere. $I_{2}=\left[\begin{array}{ll} 1 & 0\\ 0 & 1 \end{array}\right]$