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If a = [ 3 − 4 1 − 1 ] , Show that a − at is a Skewsymmetric Matrix. - Mathematics

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Question

If \[A = \begin{bmatrix}3 & - 4 \\ 1 & - 1\end{bmatrix}\] , show that A − AT is a skewsymmetric matrix.
 

 

Sum

Solution

\[Given: \hspace{0.167em} A = \begin{bmatrix}3 & - 4 \\ 1 & - 1\end{bmatrix}\] 
\[ A^T = \begin{bmatrix}3 & 1 \\ - 4 & - 1\end{bmatrix}\] 

\[Now, \] 
\[A - A^T = \begin{bmatrix}3 & - 4 \\ 1 & - 1\end{bmatrix} - \begin{bmatrix}3 & 1 \\ - 4 & - 1\end{bmatrix}\] 

\[ \Rightarrow A - A^T = \begin{bmatrix}3 - 3 & - 4 - 1 \\ 1 + 4 & - 1 + 1\end{bmatrix}\] 
\[ \Rightarrow A - A^T = \begin{bmatrix}0 & - 5 \\ 5 & 0\end{bmatrix} . . . \left( 1 \right)\] 

\[ \left( A - A^T \right)^T = \begin{bmatrix}0 & - 5 \\ 5 & 0\end{bmatrix}^T \] 
\[ \Rightarrow \left( A - A^T \right)^T = \begin{bmatrix}0 & 5 \\ - 5 & 0\end{bmatrix}\] 
\[ \Rightarrow \left( A - A^T \right)^T = - \begin{bmatrix}0 & - 5 \\ 5 & 0\end{bmatrix}\] \[ \Rightarrow \left( A - A^T \right)^T = - \left( A - A^T \right) \left[ \text{From eq .} \left( 1 \right) \right]\] 

Thus, `(A -A^T)`    is a skew  symmetric matrix.

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Chapter 5: Algebra of Matrices - Exercise 5.5 [Page 61]

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RD Sharma Mathematics [English] Class 12
Chapter 5 Algebra of Matrices
Exercise 5.5 | Q 2 | Page 61

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