Heres the equation to which where you'll need to plug in x and y

(-2y)(-2x) - [1 -2x -2y]

plug these in the equation given above... (x=1/3, y=1/3)

the answer is 1/3 but idk how the book got that answer...

here what I have so far after plugging in the x and y into the equation...

= (-2/3)(-2/3) - [1 - 2/3 - 2/3]

= 4/9 - [1 - 4/3]..... IM STUCK HERE..... did i do anything wrong??