Given: A and B are symmetric matrices
A symmetric matrix equals its own transpose: A=AT and B=BT
Let M=AB−BA
Taking the transpose:
MT=(AB−BA)T
MT=(AB)T−(BA)T
Using the transpose property (PQ)T=QTPT:
MT=BTAT−ATBT
Since A and B are symmetric, AT=A and BT=B:
MT=BA−AB
MT=−(AB−BA)
MT=−M
Since MT=−M, the matrix AB−BA is a skew-symmetric matrix.