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 AA 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 AA has two rows\blueD{\text{two rows}} and three columns\goldD{\text{three columns}}, we write its dimensions as 2×3\blueD2 \times \goldD3, pronounced "two by three".
In contrast, matrix BB has three rows\blueD{\text{three rows}} and two columns\goldD{\text{two columns}}, so it is a 3×2\blueD3\times \goldD2 matrix.
B=[8423121810]B=\left[\begin{array}{rr}-8 & -4 \\ 23 & 12 \\18 &10 \end{array}\right]
When working with matrix dimensions, remember rows×columns\blueD{\text{rows}} \times \goldD{\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 GG:
G=[41471851320422]G=\left[\begin{array}{rr}4& 14&-7 \\ 18 & 5&13 \\-20 &4&22 \end{array}\right]
The element g2,1g_{\blueD2,\goldD1} is the entry in the second row\blueD{\text{second row}} and the first column\goldD{\text{first column}}.
In this case g2,1=18g_{2,1}=\maroonD{18}.
In general, the element in row i\blueD{\text{row } i} and column j\goldD{\text{column }j} of matrix AA is denoted as ai,ja_{\blueD i,\goldD j}.

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