# Intro to matrices

Matrix is an arrangement of numbers into rows and columns. Make your first introduction with matrices and learn about their dimensions and elements.

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**matrix**is a rectangular arrangement of numbers into rows and columns.For example, matrix $A$ has two

**rows**and three**columns**.## Matrix dimensions

The

**dimensions**of a matrix tells its size: the number of rows and columns of the matrix,*in that order*.Since matrix $A$ has $\blueD{\text{two rows}}$ and $\goldD{\text{three columns}}$, we write its dimensions as $\blueD2 \times \goldD3$, pronounced "two by three".

In contrast, matrix $B$ has $\blueD{\text{three rows}}$ and $\goldD{\text{two columns}}$, so it
is a $\blueD3\times \goldD2$ matrix.

When working with matrix dimensions, remember $\blueD{\text{rows}} \times \goldD{\text{columns}}$!

### Check your understanding

## Matrix elements

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**matrix element**is simply a matrix entry. Each element in a matrix is identified by naming the row and column in which it appears.For example, consider matrix $G$:

The element $g_{\blueD2,\goldD1}$ is the entry in the $\blueD{\text{second row}}$ and the $\goldD{\text{first column}}$.

In this case $g_{2,1}=\maroonD{18}$.

In general, the element in $\blueD{\text{row } i}$ and $\goldD{\text{column }j}$ of matrix $A$ is denoted as $a_{\blueD i,\goldD j}$.