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4.6IDENTITY MATRIX LOH HUI YI CHANG WAN LING LEE CHAI EN  KAM SIEW HUEY
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
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.
  A matrix with the same number of rows and columns is called a squarematrix. 3x3
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
EXAMPLE 1 1  2     1  1         3  7         3  4     1  1         3  7           so     1  1          1  1   is not an identity matrix
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
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
              -4   -3      If M =  -6    5   ,then find      M×I, where I is an identity matrix.
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) ×
Step 4: =    -4   -3                     -6   5      (Simplifying) Step 5: Hence M×I = M =   -4  -3                                                -6   5   #

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Identity matrix

  • 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 #