what will happen on adding an upper triangular matrice and lower triangular matrice

Dear student, 
On adding upper triangle and lower triangle matrices 
the principle diagonal elements of two matrices added up and elements above the principle diagonal in the resultant matrix is  the elements of upper triangle elements which are above the principle diagonal of the upper triangle matrix,elements below the principle diagonal of the resultant matrix is the elements of lower triangle matrices which are below the principle diagonal of lower triangle matrix

regards