Question 752885
This is done by completing the square.
  3x^2 - 6x + 12
Move the 12 to the right, leaving
the 3x^2 - 6x on the left

   3x^2 - 6x     +12
Take out 3 from 3x^2 -6x

  3(x^2 - 2x)    +12
The number in front of the x
halve and multiply by itself

  -2 => -1 => -1^2 = 1
Place this at the end of 
3(x^2 - 2x + 1)     +12

Now (x^2 - 2x + 1) can be
converted to (x - 1)^2

So we have:
3(x - 1)^2 

Now to balance placing the +1
in the left hand bracket we add
3 x -1 = -3 to the right hand
side.
This gives us:-
3(x - 1)^2 + 9
If there is a negative x placed in
the formula the square will convert
it to a positive value.
Hope this helps
:-)