Answer:
y = - (x - 3)² + 15
Step-by-step explanation:
using the method of completing the square
y = x² + 6x + 6 ← factor out - 1 from the first 2 terms
y = - (x² - 6x) + 6
to complete the square
add/subtract ( half the coefficient of the x- term )² to x² - 6x
y = - (x² + 2(- 3)x + 9 - 9) + 6
= - (x - 3)² + 9 + 6
= - (x - 3)² + 15
