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If A is a singular matrix, then A adj (A)
  • a)
    is an identity matrix
  • b)
    is a zero scalar
  • c)
    is a scalar matrix
  • d)
    is an orthogonal matrix
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
If A is a singular matrix, then A adj (A)a)is an identity matrixb)is a...
Explanation:
To understand why A adj(A) is a zero scalar matrix when A is a singular matrix, let us first understand what is a singular matrix and what is an adjoint matrix.

Singular Matrix:
A matrix is said to be singular if it does not have an inverse. That is, if A is a square matrix of order n, then A is said to be singular if det(A) = 0.

Adjoint Matrix:
The adjoint matrix of a square matrix A of order n is denoted by adj(A) and is defined as the transpose of the matrix of co-factors of A. That is,

adj(A) = [C]T

where C is the matrix of co-factors of A.

Now, let us consider the product A adj(A), where A is a singular matrix.

A adj(A) = A [C]T

= [AC]T

= [det(A) I]T

= det(A) I

where I is the identity matrix of order n.

Since A is a singular matrix, det(A) = 0.

Therefore, A adj(A) = 0 I = 0.

Hence, the correct option is B: A adj(A) is a zero scalar matrix when A is a singular matrix.
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If A is a singular matrix, then A adj (A)a)is an identity matrixb)is a zero scalarc)is a scalar matrixd)is an orthogonal matrixCorrect answer is option 'B'. Can you explain this answer?
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