If A is symmetric as well as skew symmetric matrix, then A is
Let A = [aij]
Since A is skew-symmetric,
aii = 0 and aij = –aji (i ≠ j)
A is symmetric as well, so aij = aji for all i and j.
aij = 0 for all i ≠ j
Hence, aij = 0 for all i and j i.e. A is a null matrix.