Compute big D and classify the critical points in the table below

(a,b)  |  f | f_x | f_y | f_xx | f_yy | f_xy 
---------------------------------------------
(0,0)  | 25 |  0  |  0  |  2   |  4   |  1   
---------------------------------------------
(1,0)  | 12 |  0  |  0  |  4   |  0   |  2   
---------------------------------------------
(2,1)  |  3 |  0  |  0  |  -2  |  -3  |  2   
---------------------------------------------
(2,2)  | 13 |  0  |  0  |  0   |  4   |  -7  


Answer
(a,b)  |  f | f_x | f_y | f_xx | f_yy | f_xy |  D  | classification
-------------------------------------------------------------------
(0,0)  | 25 |  0  |  0  |  2   |  4   |  1   |  7  | u -- loc min
-------------------------------------------------------------------
(1,0)  | 12 |  0  |  0  |  4   |  0   |  2   | -4  | saddle
-------------------------------------------------------------------
(2,1)  |  3 |  0  |  0  |  -2  |  -3  |  2   |  2  | n -- loc max
-------------------------------------------------------------------
(2,2)  | 13 |  0  |  0  |  0   |  4   |  -7  | -49 | saddle