Answer:
vertex = (4, - 16 )
Step-by-step explanation:
Given a quadratic in standard form, f(x) = ax² + bx + c : a ≠ 0
Then the x- coordinate of the vertex is
[tex]x_{vertex}[/tex] = - [tex]\frac{b}{2a}[/tex]
f(x) = x² - 8x - 9 ← is in standard form
with a = 1, b = - 8, thus
[tex]x_{vertex}[/tex] = - [tex]\frac{-8}{2}[/tex] = 4
Substitute x = 4 into f(x) for corresponding y- coordinate
f(4) = 4² - 8(4) - 9 = 16 - 32 - 9 = - 16
vertex = (4, - 16 )
