Compute the determinants in cofactor expansions. At each step, choose a row or column that involves the least amount of computation.
![1068_64fea66b-a689-4d2d-ab11-e2c668547b1d.png](https://secure.tutorsglobe.com/CMSImages/1068_64fea66b-a689-4d2d-ab11-e2c668547b1d.png)
The expansion of a 3 X 3 determinant can be remembered by the following device. Write a second copy of the first two columns to the right of the matrix, and compute the determinant by multiplying entries on six diagonals:
![1253_fb037075-04dd-4849-a84a-c0fe59578da3.png](https://secure.tutorsglobe.com/CMSImages/1253_fb037075-04dd-4849-a84a-c0fe59578da3.png)