Consider the quadratic function:

f(x) = x2 – 8x – 9

vertex: (startfraction negative b over 2 a endfraction, f (startfraction negative b over 2 a))

what is the vertex of the function?

(4, -25)

Step-by-step explanation:

One thing I wanted to say is thank you for including the equation to find the vertex! I literally had a brain fart and was like wait it is -b over 2a, then I looked and high fived myself lol but anyways. But anyways the question is what is the vertex of x²-8x-9??

First let's label this formula. The quadratic formula has three variables to label and it labels them as a,b, and c.

a= x²   b= -8   c=-9  ( and yes the negative and positive sign makes a difference, trust me. :D )

So again what is the vertex equation? It is -b over 2a. So let's look at our functiion and plug in the numbers.

b= -8  => -b= -(-8) = +8

a= 1  =>   2a= 2(1) = 2

So -b/2a equals a positive 8 divided by 2. 8 divided by two equals.. 4.

Yet what would be outcome of this equation. How about we input 4 into the equation we have.

f(x)= x²-8x-9

f(4)= (4)²-8(4)-9

f(4)= 16-(32)-9

f(4)= -16-9

f(4)= -25

So in this case (4, -25) is the vertex of this equation!!

Sorry for typing so much, I know it may be alot, but it's the answer. Yet, I really do hope I gave you a very clear answer. If you have any questions or comment, don't be afraid to say ask or even message me. If you have to. But anyways I hoped I help, have a great day!! :D