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### Course: Algebra (all content) > Unit 20

Lesson 1: Introduction to matrices# 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.

A

**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 ${\text{two rows}}$ and ${\text{three columns}}$ , we write its dimensions as ${2}\times {3}$ , pronounced "two by three".

In contrast, matrix $B$ has ${\text{three rows}}$ and ${\text{two columns}}$ , so it
is a ${3}\times {2}$ matrix.

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

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## Matrix elements

A

**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 ${g}_{{2},{1}}$ is the entry in the ${\text{second row}}$ and the ${\text{first column}}$ .

In this case ${g}_{2,1}={18}$ .

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

### Check your understanding

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