1) A singular matrix has a determinant of 0, while a non-singular matrix has a non-zero determinant. 2) A symmetric matrix is equal to its transpose, while a skew-symmetric matrix is equal to the negative of its transpose. 3) The adjoint of a matrix is obtained by swapping diagonal entries and changing the sign of non-diagonal entries. For 3x3 matrices, the adjoint is the transpose of the cofactors.