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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Matrices

NDA 2025 · Mathematics · Matrices

If A = pmatrix x & y & z y & z & x z & x & y pmatrix where x , y ,...

If A=(xyzyzxzxy)A = \begin{pmatrix} x & y & z \\ y & z & x \\ z & x & y \end{pmatrix} where xx, yy, zz are integers, is an orthogonal matrix, then what is A2A^2 equal to?

Options

  1. ANull matrix
  2. BIdentity matrix
  3. CAA
  4. D−A-A

Correct answer

B. Identity matrix

Step-by-step solution

Given the matrix A=(xyzyzxzxy)A = \begin{pmatrix} x & y & z \\ y & z & x \\ z & x & y \end{pmatrix}.

The transpose of AA is given by:

AT=(xyzyzxzxy)A^T = \begin{pmatrix} x & y & z \\ y & z & x \\ z & x & y \end{pmatrix}

We can observe that AT=AA^T = A, which means AA is a symmetric matrix.

It is given that AA is an orthogonal matrix. By the definition of an orthogonal matrix, we have:

AAT=IA A^T = I

Substituting AT=AA^T = A into the above equation, we get:

AA=IA A = I

A2=IA^2 = I

Thus, A2A^2 is equal to the identity matrix.

Answer: Identity matrix
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