Many people know this mnemonic for the determinant of a 3 × 3 matrix: first repeat the first two columns and then sum the products on the forward diagonals and subtract the products on the backward diagonals. That is, first write

and then calculate this.
h1,1h2,2h3,3 + h1,2h2,3h3,1 + h1,3h2,1h3,2
-h3,1h2,2h1,3 - h3,2h2,3h1,1 - h3,3h2,1h1,2
(a) Check that this agrees with the formula given in the preamble to this section.
(b) Does it extend to other-sized determinants?

, 1,1 hi,.2 2,1 h2.2 2,32, hz,2 11m