Answer:
y = 8(x - 9)² - 8
Explanation:
A quadratic function in vertex form is
y = a(x - h)² + k
(h, k ) are the coordinates of the vertex and a is a multiplier
given
y = 8x² - 144x + 640 ← in standard form
using the method of completing the square to obtain vertex form
Before applying the method we require the coefficient of the x² term to be 1
factor out a common factor of 8 from the first 2 terms
y = 8(x² - 18x) + 640
add/subtract ( half the coefficient of the x- term)² to x² - 18x
y = 8(x² + 2(- 9)x + 81 - 81) + 640
= 8(x - 9)² + 8(- 81) + 640
= 8(x - 9)² - 648 + 640
= 8(x - 9)² - 8 ← in vertex form