Answer:
vertex = (10, - 80 )
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
y = x² - 20x + 20
Using the method of completing the square
add/subtract ( half the coefficient of the x- term )² to x² - 20x
y = x² + 2(- 10)x + 100 - 100 + 20
= (x - 10)² - 80 ← in vertex form
vertex = (10, - 80 )