What is the vertex of g(x) = 8x2 – 64x?

(4, –128)
(–4, –128)
(4, –16)
(–4, –16)

Question

What is the vertex of g(x) = 8x2 – 64x?

(4, –128)
(–4, –128)
(4, –16)
(–4, –16)

serenity74 · Answer

solve for x and solve for f(x) (aka y)

priyar · Answer

use completing the square..

campbell_st · Answer

all you need to do is find the line of symmetry. The vertex lines on the line of symmetry

for a parabola 

$$y = ax^2 + bx + c$$

the line of symmetry is 

$$x = \frac{-b}{2a}$$

you  have a = 8 and b = -64 

when you find the line of symmetry, x value in the vertex

substitute it into the original equation to find the the corresponding y- value

so the vertex is (x, f(x)) 

hope it helps

campbell_st · Answer

another method is to factor and the line of symmetry is midway between the two zeros

then substitute it to find f(x)