Question

On the graph of a quadratic function, the x-intercepts are (4, 0) and (8, 0), and the vertex is (6, −4). Which equation represents the function?

Answer 1

A

Explanation:

given the x- intercepts x = a and x = b then the corresponding factors are

(x - a) and (x - b)

the equation of the quadratic is then the product of the factors , that is

y = a(x - a)(x - b) ← a is a multiplier

here the x- intercepts are x = 4 and x = 8 , then factors are

(x - 4) and (x - 8 ) , so

y = a(x - 4)(x - 8)

to find a substitute any other point on the graph into the equation

given vertex = (6, - 4 ) , then

- 4 = a(6 - 4)(6 - 8)

- 4 = a(2)(- 2) = - 4a ( divide both sides by - 4 )

1 = a , then

y = (x - 4)(x - 8) ← expand using FOIL

y = x² - 12x + 32