i use this every time.consider 1  2  3

                                           4  5  6

                                           7  8  9

write this as 5  4  6   5(starting from the middle)

                  8   7  9   8

                  2   3  1   2

                  5   4   6  5

 

now multiply like(35-42)(like the determinant) and enter the values as

 

                    -3    -6    3 

                    10   -20   10 (and so on)

taking the transpose gives u adjoint and then u can find the inverse.