matrix
a rectangular array of number
its size is row x column or m x n
-------> this is a 2 x 3 matrix
matix with same number of columns and rows is called square matrix

2 types of matrix coefficient and augmented
coefficient matrix-- matrix which only the coefficient of the variables in the given system is written
x+9y-13z=2
20x+5y+-6z=9

augmented matrix-- matrix which the constant is written
x+9y-13z=2
20x+5y+-6z=9