Question

Which equation represents y = x^2 − 8x + 5 in vertex form?

A) y = (x − 4)^2 − 9


B) y = (x − 4)^2 + 11


C) y = (x − 4)^2 + 21


D) y = (x − 4)^2 − 11

Answer 1

answer: D) y=(x-4)^2-11

by completing the square:
y=x^2-8x+5
y=x^2-8x+16+5-16
y=(x-4)^2-11

where did we get 16?
(-8/2)^2=16

Answer 2

Answer: D

Explanation:

y = x² - 8x + 5

-5 -5

y - 5 = x² - 8x complete the square by adding
`((-8)/(2))^(2)` to both sides

y - 5 + 16 = x² - 8x + 16 the right side is a perfect square: (x - 4)²

y + 11 = (x - 4)²

-11 -11

y = (x - 4)² - 11