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If a matrix A=[3−57524−7−49]A=\begin{bmatrix} 3 & -5 & 7 \\ 5 & 2 & 4 \\ -7 & -4 & 9 \end{bmatrix} is expressed as the sum of a symmetric matrix P and a skew symmetric matrix Q, then symmetric matrix P will be

Solution

✅ Correct Option: 3

The symmetric part is P=12(A+AT)P = \dfrac{1}{2}(A+A^T).

Here A+AT=[6000400018]A + A^T = \begin{bmatrix} 6 & 0 & 0 \\ 0 & 4 & 0 \\ 0 & 0 & 18 \end{bmatrix}, since the off-diagonal entries of AA are equal and opposite.

So P=[300020009]P = \begin{bmatrix} 3 & 0 & 0 \\ 0 & 2 & 0 \\ 0 & 0 & 9 \end{bmatrix}, which is a diagonal matrix.

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