Question:
If $A$ and $B$ are two skew-symmetric matrices of same order, then $A B$ is symmetric if______
Solution:
It is given that, $A$ and $B$ are two skew-symmetric matrices of same order.
$\therefore A^{T}=-A$ and $B^{T}=-B$ ....(1)
Now, the matrix $A B$ is symmetric if
$(A B)^{T}=A B$ (A matrix $X$ is symmetric if $X^{T}=X$ )
$\Rightarrow B^{T} A^{T}=A B$
$\Rightarrow(-B)(-A)=A B \quad[$ Using (1) $]$
$\Rightarrow B A=A B$
Thus, if $A$ and $B$ are two skew-symmetric matrices of same order, then $A B$ is symmetric if $A B=B A$.
If $A$ and $B$ are two skew-symmetric matrices of same order, then $A B$ is symmetric if $A B=B A$