Answer:
(x -6)²
Step-by-step explanation:
It is worth remembering the form of the square of a binomial:
(a +b)² = a² +2ab +b²
Note that if "a" and "b" have different signs, the middle term will be negative.
In your case, the square root of the constant is half the magnitude of the x-coefficient, so the trinomial you have is a perfect square. Since you just found √36 = 6, and the sign of 12 tells you the terms have different signs, you know the answer is ...
x² -12x +36 = (x -6)²
_____
Of course, you recognize (x +6)(x -6) as the factoring of the difference of squares ...
x² -6² = x² -36
which is not what you have.
