Convert y =(x+1)(x-9) to vertex form

y = (x - 4)² - 25

Step-by-step explanation:

The equation of a parabola in vertex form is

y = a(x - h)² + k

where (h, k) are the coordinates of the vertex and a is a multiplier

To obtain this form use the method of completing the square.

Given

y = (x + 1)(x - 9) ← expand factors using FOIL, thus

y = x² - 8x - 9

To complete the square

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

y = x² + 2(- 4)x + 16 - 16 - 9

  = (x - 4)² - 25 ← in vertex form

step-by-step explanation: