the point states that the sum of the product of any two rows or columns (i.e, the product of all the elements of one row(cols)+ product of all elements of another row(cols) )
in the above example, lets take 1st and 2ns rows
product of first row elements = (cos x) (-sin x) (0) =0
product of second row elements = (-sin x) (cos x)(0) =0
their sum (1st row +2nd row) =0
