Question

Given an example of
(i) a row matrix which is also a column matrix,
(ii) a diagonal matrix which is not scalar,
(iii) a triangular matrix

Answer 1

$\left(i\right)\left[\begin{array}{c}6\end{array}\right]$
This is a matrix that contains only one element.

$\left(ii\right)\left[\begin{array}{ccc}1& 0& 0\\ 0& 2& 0\\ 0& 0& 3\end{array}\right]$

For a diagonal matrix which is not scalar, all elements except those in the leading diagonal should be zero and the
elements in the diagonal should not be equal.

$\left(iii\right)\left[\begin{array}{ccc}1& 2& 3\\ 0& 5& 4\\ 0& 0& 6\end{array}\right]$

Here, all elements below the main diagonal in upper triangular matrix are zero.

$\left[\begin{array}{ccc}1& 0& 0\\ 2& 6& 0\\ 3& 4& 5\end{array}\right]$

Here, all elements above the main diagonal in lower triangular matrix are zero.