Solve x2 - 12x + 5 = 0 by completing the square.

which equation is used in the process?

(x - 6)2 = 31 ,
(x - 6)2 = 26 ,
(x - 6)2 = 19

The answer would be the first one, (x-6)^2=31. To explain this
first, you must expand and simplify the equation and it would look like this,
(x-6)(x-6)=31. Then, solve and simplify the equation and will look like this, "x^2 - 12x + 36 = 31". Since 36 and 31 can be simplified more.
Just transpose 31 to the left and it will become negative and it will look like this,
x^2 + 12x + 36 - 31 = 0
Then the answer would be x^2 + 12x + 5 = 0