When some group of numbers are arranged in a rectangular form, and its form of horizontal & vertical lines and these are enclosed by brackets [ ] or parenthesis ( ), is called a matrix. The horizontal lines in a matrix are called its rows, and the vertical lines in it are called its columns.
The numbers constituting a matrix are called its elements or entries. The plural of matrix is called matrices.
Order of a Matrix –
A matrix having m rows and n columns is called an (m X n) [should read as m by n] matrix or a matrix of order m by n.
Clearly, an (m X n) matrix has mn elements.
We denote matrices by capital letters. An element of a matrix appearing in i-th row and j-th column is called the (I, j)th element of the matrix.
This above matrix has 3 rows and 6 columns. So, its order is (3 X 6) [3 by 6]
Number of elements in A = (3 X 6) = 18 (Ans.)
This above matrix has 5 rows and 3 columns. So, its order is (5 X 3) [3 by 6]
Number of elements in A = (5 X 3) = 15 (Ans.)
Your second block of text...