The determinant is .

Step 1:

Rewrite the first two columns to the right of the determinant.

         (Original determinant)

Step 2:

Find the product of the elements of the diagonals.

First group diagonals. 

                 (Multiply first group diagonals)

                 (Multiply second group diagonals)

Step 3:

Find the sum of each group.

Sum of the first group diagonals .

Sum of the second group diagonals .

Step4:

Subtract the sum of the second group from the sum of the first group.

.

The determinant value is .