## Elementary Questions about a Matrix

## Problem 693

Let

\[A=\begin{bmatrix}

-5 & 0 & 1 & 2 \\

3 &8 & -3 & 7 \\

0 & 11 & 13 & 28

\end{bmatrix}.\]

**(a)** What is the size of the matrix $A$?

**(b)** What is the third column of $A$?

**(c)** Let $a_{ij}$ be the $(i,j)$-entry of $A$. Calculate $a_{23}-a_{31}$.