Question

The first three steps in writing f(x) = 40x + 5x2 in vertex form are shown.

Write the function in standard form. f(x) = 5x2 + 40x
Factor a out of the first two terms. f(x) = 5(x2 + 8x)
Form a perfect square trinomial. (eight-halves) squared = 16
f(x) = 5(x2 + 8x + 16) – 5(16)
What is the function written in vertex form?

f(x) = 5(x + 4) – 80
f(x) = 5(x + 8) – 80
f(x) = 5(x + 4)2 – 80
f(x) = 5(x + 8)2 – 80

Answer 1

3. f(x) = 5(x + 4)2 – 80

Explanation:

Answer 2

third option

Explanation:

Given

f(x) = 40x + 5x² ← express in standard form

f(x) = 5x² + 40x ← factor out 5 from each term

f(x) = 5(x² + 8x)

To complete the square

add/ subtract ( half the coefficient of the x- term)² to x² + 8x

f(x) = 5(x² + 2(4)x + 16 - 16)

f(x) = 5(x + 4)² + 5(- 16)

f(x) = 5(x + 4)² - 80