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3 votes
Consider the quadratic function:

f(x) = x2 – 8x – 9

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

1 Answer

6 votes

Answer:

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.

User DLee
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