What is the vertex of the function: f (x) = (x + 4) (x - 2)?

Question

A. (-1, -9)

B. (0, -8)

C. (-4, 2)

D. (4, -2)

Answer 1

f(x)= (x+4)(x-2) has x intercepts 2 and -4. The average is the x coordinate of the vertex: (2-4)/2 =-2/2 = -1

A) is the correct answer, as it's the only answer with an x coordinate of -1

It's an upward opening parabola so the vertex has a y coordinate <0.

(x+4)(x-2) = x^2 +2x -8

complete the square: x^2 +2x +1, -8 -1

(x+1)^2 -9 is in the form a(x-h)^2 +k where (h,k) is the vertex, (-1,-9)