Question

3. What is the vertex of the graph of the

function f(x) = x2 + 8x?
A (-4, 16) B (0,8)
C(-4, -16) D(0, -8)
-

Answer 1

A

Explanation:

Given a parabola in standard form

f(x) = ax² + bx + c ( a ≠ 0 )

then the x- coordinate of the vertex is

x = -
`(b)/(2a)`

f(x) = x² + 8x ← is in standard form

with a = 1 , b = 8 , then

x = -
`(8)/(2)` = - 4

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

f(- 4) = (- 4)² + 8(- 4) = 16 - 32 = - 16

vertex = (- 4, - 16 ) → A