Answer:
9
Step-by-step explanation:
When the leading coefficient (the coefficient of the x² term) is 1, we can complete the square by taking the b coefficient (coefficient of the x term), dividing it by 2, squaring the result, and adding it to both sides.
b = -6
b/2 = -3
(b/2)² = 9
Add 9 to both sides to make the left side a perfect-square trinomial.
