Definition Of Identity Matrix

A square matrix in which all the main diagonal elements are 1's and all the remaining elements are 0's is called an Identity Matrix.

More About Identity Matrix

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

Video Examples: The Identity Matrix
 

Example of Identity Matrix

are identity matrices of order 1×1, 2×2, 3×3,....n×n.

Solved Example on Identity Matrix

Ques: If M = , then find M×I, where I is an identity matrix. 

Choices:

Correct Answer: B

Solution:

Step 1: M =  [Given.]
Step 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 =  ×  [Matrix Multiplication.]
Step 4: =  [Simplifying.]
Step 5: Hence M×I = M = 

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