We must understand what symmetric matrix is.

A symmetric matrix is a square matrix that is equal to its transpose.

A symmetric matrix ⬄ A = A^T

Now, let us understand what skew-symmetric matrix is.

A skew-symmetric matrix is a square matrix whose transpose equals its negative, that, it satisfies the condition

A skew symmetric matrix ⬄ A^T = -A

And,

A square matrix is a matrix with the same number of rows and columns. An n-by-n matrix is known as a square matrix of order n.

We need to find a square matrix which is both symmetric as well as skew symmetric.

Take a 2 × 2 null matrix.

Say,

Let us take transpose of the matrix A.

We know that, the transpose of a matrix is a new matrix whose rows are the columns of the original.

So,

Since, A = A^T.

∴, A is symmetric.

Take the same matrix and multiply it with -1.

Let us take transpose of the matrix –A.

So,

Since,

A^T = -A

∴, A is skew-symmetric.

Thus, A (a null matrix) is both symmetric as well as skew-symmetric.