Q168 / 270 · NDA 2026 (Phase 1) · Mathematics

Consider the following statements :
I. If $n\times n$ $(n>1)$ matrix is symmetric, then its inverse is also a symmetric matrix.
II. If $n\times n$ $(n>1)$ matrix is singular, then its adjoint is also a singular matrix.
Which of the statements given above is/are correct ?

  • A
    I only
  • B
    II only
  • Correct answer
    C
    Both I and II
  • D
    Neither I nor II

Solution

Let $A$ be an invertible symmetric matrix of order $n \times n$. Then $A^T = A$.

We know that $(A^{-1})^T = (A^T)^{-1}$.

Substituting $A^T = A$, we get $(A^{-1})^T = A^{-1}$.

Thus, the inverse of a symmetric matrix is also symmetric. The first statement is correct.

Let $A$ be a singular matrix of order $n \times n$. Then $|A| = 0$.

The determinant of the adjoint of $A$ is given by $|\text{adj}(A)| = |A|^{n-1}$.

Since $n > 1$ and $|A| = 0$, we have $|\text{adj}(A)| = 0^{n-1} = 0$.

Thus, the adjoint of a singular matrix is also a singular matrix. The second statement is correct.

Both statements are correct.

Answer: Both I and II

Hence, the correct answer is option: 'C'.

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