Answer:
y = - x² + 8x - 16
Step-by-step explanation:
since x = 4 is a root of multiplicity 2 then
(x - 4)² are the factors, and
y = a(x - 4)² ← where a is a multiplier
here leading coefficient is - 1 ⇒ a = - 1
y = -(x - 4)² ( expand and multiply by - 1 )
y = -(x² - 8x + 16) = - x² + 8x - 16