Answer:
y=(x-6)^2-21
Explanation:
To complete the square, the same value needs to be added to both sides
y+?=x^2-12x+?+15
To complete the square x^2-12x+36=(x-6)^2 add 36 to the expression
y+?=x^2-12x+36+15
Since 36 was added to the right-hand side, also add 36to the left-hand side
y+36=x^2-12x+36+15
Use a^2-2ab+b^2=(a-b)^2 to factor the expression
y+36=(x-6)^2+15
Move the constant to the right-hand side and change its sign
y=(x-6)^2+15-36
Calculate the difference
y=(x-6)^2-21
