Question

Consider the quadratic function:

f(x) = x2 – 8x – 9



Vertex:

What is the vertex of the function?

Answer 1

(4, - 25)

Explanation:

Given a quadratic in standard form : ax² + bx + c : a ≠ 0

Then the x- coordinate of the vertex is

`x_(vertex)` = -
`(b)/(2a)`

f(x) = x² - 8x - 9 is in standard form

with a = 1, b = - 8 and c = - 9, thus

`x_(vertex)` = -
`(-8)/(2)` = 4

Substitute x = 4 into f(x) for corresponding y- coordinate

f(4) = 4² - 8(4) - 9 = 16 - 32 - 9 = - 25

Vertex = (4, - 25)