Completing the square follows the principle of taking 
and converting it into 
where d is the 'correctional number' as I like to call it - i.e. the number that converts the expanded bracket into the +c, since the expanded bracket will give us 
.
In this case, 2/2=1 so we have the first part:
.
Expanding this gives us
. We need c to be 9, so we can just add 8.
Putting this together:
Now we can solve it more easily.
Rearranging:
In this case, 2/2=1 so we have the first part:
Expanding this gives us
Putting this together:
Now we can solve it more easily.
Rearranging: