# What is the dimension of the matrix [(17,-2,8,-9,6), (5,11,20,-1,4)]?

Dec 2, 2016

This is a $2 \times 5$ matrix (pronounced "two by five").

#### Explanation:

A matrix is size $a \times b$ if it has $a$ rows and $b$ columns. Another way of thinking about this is that it is $\text{rows}$ $\times$ $\text{columns}$.

A way to remember that the order is "rows, columns" is that it sounds like Roman columns.

The given matrix has two rows, which are horizontal, and five columns, which are vertical.

If you're still confused:

$\left[\begin{matrix}\textcolor{red}{17} & \textcolor{red}{- 2} & \textcolor{red}{8} & \textcolor{red}{- 9} & \textcolor{red}{6} \\ \textcolor{b l u e}{5} & \textcolor{b l u e}{11} & \textcolor{b l u e}{20} & \textcolor{b l u e}{- 1} & \textcolor{b l u e}{4}\end{matrix}\right]$ $\left.\begin{matrix}\text{ "larr" "color(red)1 \\ " "larr" } \textcolor{b l u e}{2}\end{matrix}\right.$

One row is in red, and the other row is in blue.

The five columns are sorted by color:

$\left[\begin{matrix}\textcolor{red}{17} & \textcolor{b l u e}{- 2} & \textcolor{g r e e n}{8} & \textcolor{v i o \le t}{- 9} & \textcolor{\mathmr{and} a n \ge}{6} \\ \textcolor{red}{5} & \textcolor{b l u e}{11} & \textcolor{g r e e n}{20} & \textcolor{v i o \le t}{- 1} & \textcolor{\mathmr{and} a n \ge}{4}\end{matrix}\right]$

$\textcolor{w h i t e}{\begin{matrix}\textcolor{b l a c k}{\uparrow} & \textcolor{b l a c k}{\uparrow} & \textcolor{b l a c k}{\uparrow} & \textcolor{b l a c k}{\uparrow} & \textcolor{b l a c k}{\uparrow} \\ \textcolor{red}{1} & \textcolor{b l u e}{2} & \textcolor{g r e e n}{3} & \textcolor{v i o \le t}{4} & \textcolor{\mathmr{and} a n \ge}{5}\end{matrix}}$