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

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

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:

 and

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

Filling in for h:

 simplifies to

Filling in for k:

 which simplifies a bit to

 which simplifies a bit more to

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.

for ex: the reciprocal of 3/4 is 4/3. it is the opposite.

reciprocal definition:

a mathematical expression or function so related to another that their product is one; the quantity obtained by dividing the number one by a given quantity.