# Chapter 3 Matrices

Matrix is one of the most fundamental chapters of Mathematics, which will help us not only in mathematics but also in other branches like mechanics, optics, computer science, etc. It solves tedious calculations very easily. Topics incorporated in this chapter are notation, order, types and equality of matrix, zero matrix, transpose, symmetric and skew symmetric matrices, addition and multiplication of matrices, properties, row and column operations, Invertible matrices and proof of uniqueness of inverse, if it exists.

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### Exercise 1

•  Q2 If a matrix has 24 elements, what are the possible order it can have? What, if it has 13 elements? Ans: We know that if a matrix is of the order m × n, it has mn elements. Thus, to find all the possible orders of a matrix having 24 elements, we have to find all the ordered pairs of natural numbers whose product is 24. The ordered pairs are: (1, 24), (24, 1), (2, 12), (12, 2), (3, 8), (8, 3), (4, 6), and (6, 4) Hence, the possible orders of a matrix having 24 elements are: 1 × 24, 24 × 1, 2 × 12, 12 × 2, 3 × 8, 8 × 3, 4 × 6, and 6 × 4 (1, 13) and (13, 1) are the ordered pairs of natural numbers whose product is 13. Hence, the possible orders of a matrix having 13 elements are 1 × 13 and 13 × 1. Q3 If a matrix has 18 elements, what are the possible orders it can have? What, if it has 5 elements? Ans: We know that if a matrix is of the order m × n, it has mn elements. Thus, to find all the possible orders of a matrix having 18 elements, we have to find all the ordered pairs of natural numbers whose product is 18. The ordered pairs are: (1, 18), (18, 1), (2, 9), (9, 2), (3, 6,), and (6, 3) Hence, the possible orders of a matrix having 18 elements are: 1 × 18, 18 × 1, 2 × 9, 9 × 2, 3 × 6, and 6 × 3 (1, 5) and (5, 1) are the ordered pairs of natural numbers whose product is 5. Hence, the possible orders of a matrix having 5 elements are 1 × 5 and 5 × 1.