Dimensions of a Matrix and Multiplying Matrices

This is a matrix. A matrix has rows and columns.





Rows are horizontal...

and columns are vertical.

In order to write a dimensions statement, you gotta count the number of ROWS and then number of COLUMNS.

 This is a 3x3 matrix because it has 3 rows and 3 columns. Also known as a square matrix and the identity matrix. 



This is a 3x3 column because it has 3 rows and 3 columns. Also known as a square matrix because it has the same number of rows and columns.

This is a 1x3 matrix because it has 1 row and 3 columns.



This is a 2x2 matrix because it has 2 rows and 2 columns. Also known as a square matrix.

By knowing the dimensions statement, you can figure out if you can multiply two matrices or not. For example, you can multiply a 3x2 matrix and a 2x5 matrix because the two inside numbers are the same. The answer will be a 3x5 matrix because the two outside numbers always give you your answer.