Question

Which among the following can be called as identity matrix/matrices.

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

Answer 1

Answer: (A), (D)

$\left[\begin{array}{ccc}1& 0& 0\\ 0& 1& 0\\ 0& 0& 1\end{array}\right]$

As we said the only condition for a matrix to become identity matrix is that its main diagonal elements should be 1 and all other elements should be zero. Its satisfied for (a) and (d). In option (b) its not the main diagonal whose elements are one hence dissatisfying the condition.