# algebra(reiny)

posted by
**Marissa** on
.

Hey thanks for all your help but you kinda confused me on a few:

1)Determine whether f(x)=-5x^2-10x+6 has a maximum or minimum value and find that value

A.minimum -1

B.maximum 11

C.maximum -1

D.minimum 11

and you said the function opens up, so there is a minimum.

it occurs when x=-1, and that minimum is f(-1), which is 11. So the answer is D right?

2)Identify the vertex,axis of symmetry,and direction of opening for y=1/2(x-8)^2+2

A.(8,2);x=-8;up

B.(-8,-2);x=-8;down

C.(8,-2);x=8;up

D.(8,2);x=8;up

I picked A,here is your reasoning.vertex is ok, but how can the axis of symmetry be x=-8?? Would it not go through the vertex?? So it is x=9 (always the same as the x of the vertex)

3)Which quadratic function has its vertex at(-2,7)and opens down?

A.y=-3(x+2)^2+7

B.y=(x-2)^2+7

C.y=-12(x+2)^2-7

D.y=-2(x-2)+7

4)Write y=x^2+4x-1 in vertex form.

A.y=(x-2)^2+5

B.y=(x+2)^2-5

C.y=(x+2)^2-1

D.y=(x+2)^2+3

Well I'm not Reiny but I can help you out with #3

I found out by plugging it into the Y=

for creating graphs on my TI-83 Plus that it is A.

You should be able to do the same if you have this calculator and plug in each function. Then hit graph

For #1 contrary to what you found I found that when I plugged it into my Y= function on my calculator that the

-curve faced down

-at X=-1 was the vertex

-Y=10.9/ 11

- based on that I would have to say my conclusion is that it has a maximum at Y=11

For #2 it is D

but not x=9 like you said but I assume it was a typo

The axis of symetry is the same as the x of the vertex (your thinking is correct)

1. yes it is D

2. I clearly meant to type x=8

3. clearly A. B would have vertex (2,7), and both C and D open downwards

4. y=x^2+4x-1

y = x^2 + 4x **+ 4 - 4** - 1

= (x+2)^2 - 5