Question

Which of the following is an upper triangular matrix?

• A. $\left[\begin{array}{ccc}5& 3& 2\\ 9& 4& 11\\ 2& -23& -7\end{array}\right]$
• B. $\left[\begin{array}{ccc}5& 3& 2\\ 0& -5& 6\\ 0& 0& 5\end{array}\right]$
• C. $\left[\begin{array}{ccc}-1& 4& 7\\ 0& 5& -8\\ 3& 0& 8\end{array}\right]$
• D. $\left[\begin{array}{ccc}5& 0& 0\\ 3.5& 1& 0\\ -7& 6& 3\end{array}\right]$

Answer 1

The correct option is B $\left[\begin{array}{ccc}5& 3& 2\\ 0& -5& 6\\ 0& 0& 5\end{array}\right]$

An upper triangular matrix is one where all entries below the main diagonal are zero.