Question

Which of the following is not an identity matrix

• A. $\left[\begin{array}{cc}1& 0\\ 0& 1\end{array}\right]$
• B. $\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& 1& 0\\ 0& 0& 0& 1\end{array}\right]$
• C. $\left[\begin{array}{ccc}1& 0& 0\\ 0& 0& 1\end{array}\right]$
• D. $\left[\begin{array}{ccc}1& 0& 0\\ 0& 1& 0\\ 0& 0& 1\end{array}\right]$

Answer 1

The correct option is C $\left[\begin{array}{ccc}1& 0& 0\\ 0& 0& 1\end{array}\right]$

An Identity Matrix is a square matrix that has $1^{\prime }s$ on the main diagonal and $0^{\prime }s$ everywhere else.