Question

Consider the quadratic function:

f(x) = x2 – 8x – 9

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

Answer 1

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=(-b)/(2a)` and

`k=c-(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=(-(-8))/(2(1))` simplifies to

`h = (8)/(2)=4`

Filling in for k:

`k=-9-((-8)^2)/(4(1))` which simplifies a bit to

`k=-9-(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.