Question

Consider the quadratic function:
f(x) = x2 – 8x – 9

Vertex:
What is the vertex of the function?
(, )

Answer 1

Answer:

Step-by-step explanation:

I'm not sure how you are finding this in class, but the easiest way by far is to use the expressions for h and k:

$h=\frac{-b}{2a}$  and

$k=c-\frac{b^2}{4a}$

(Just a fun fact:  Those expressions come from the quadratic formula that help us to factor a quadratic equation.)

Filling in for h:

$h=\frac{-(-8)}{2(1)}$  simplifies to

$h = \frac{8}{2}=4$

Filling in for k:

$k=-9-\frac{(-8)^2}{4(1)}$  which simplifies a bit to

$k=-9-\frac{64}{4}$  which simplifies a bit more to

$k=-9-16=-25$

The vertex, then, is (4, -25).

You would also find this if you completed the square.  But again, I'm not sure how you're solving for the vertex in class.