Exercise 3

The Rule of Sarrus is a mnemonic that many people learn for the $3\!\times\!3$ determinant formula. To the right of the matrix, copy the first two columns.

Then the determinant is the sum of the three upper-left to lower-right diagonals minus the three lower-left to upper-right diagonals $aei+bfg+cdh-gec-hfa-idb$. Count the operations involved in Sarrus’s formula and in Chiò’s.