From the description of first two columns of the determinant (first and second columns) will
form Scheme 1. Similarly two rows (first and second rows) form Scheme 2. The terms, which
will be formed by the products of diagonal elements in the left side in both the schemes 1 and 2
become “” sign, those in the right side become “−” sign. In this way we get the Sarrus rule,
which is valuable just to compute the determinants of the third order matrix. In base of the
Sarrus rule we have