1. 4.6IDENTITY MATRIX LOH HUI YI CHANG WAN LING LEE CHAI EN KAM SIEW HUEY

2. Definition An identity matrix, I, is a matrix which when multiplying it to another matrix, such as A, the product is the matrix A itself. IA = A and AI = A AI = IA = A

3. Identity Matrix is also called as Unit Matrix or Elementary Matrix. Identity Matrix is denoted with the letter “In×n”, where n×n represents the order of the matrix. One of the important properties of identity matrix is: A×In×n = A, where A is any square matrix of order n×n.

4. A matrix with the same number of rows and columns is called a squarematrix. 3x3

5. An identity matrix, I, is a square matrix and the elements are 0 and 1 only. The elements in the main diagonal are 1 while the others are 0. 1 0 0 0 1 0 0 0 1 I = 3 x 3

6. EXAMPLE 1 1 2 1 1 3 7 3 4 1 1 3 7 so 1 1 1 1 is not an identity matrix

7. EXAMPLE 2 1 2 1 0 1 2 3 4 0 1 3 4 so 1 0 0 1 is the identity for 2x2 matrices

8. EXERCISES 1 1 2 1 0 -2 1 0 1 2 1 0 1 2 0 1 -2 1 2 -2 1 2 -2 1

9. -4 -3 If M = -6 5 ,then find M×I, where I is an identity matrix.

10. Solution:Step 1: M = -4 -3 (Given) -6 5Step 2: As M is square matrix of order 2×2, the identity matrix I is also of same order 2×2. (Rule for Matrix Multiplication)Step 3: Then M×I = -4 -3 1 0 -6 5 0 1 = (-4x1)+(-3x0) (-4x0)+(-3x1) (-6x1)+(5x0) (-6x0)+(5x1) (Matrix Multiplication) ×

11. Step 4: = -4 -3 -6 5 (Simplifying) Step 5: Hence M×I = M = -4 -3 -6 5 #