Question

The parabola is the graph of which function? Use what you know about the parabola and vertex to help you decide.
y = -2x2 + 3x + 10
y = x2 + 6x + 10
y = -x2 - 6x - 15
y = 2x2 + 4x + 15

Answer 1

Try factoring each one, or completing the square, it'll help you decide.

Hint: it can't be either of the first two options, since they both have a positive x^2 term, and the parabola faces down, meaning there must be a negative on the x^2.

Answer 2

would it work if i find teh vertex?

Answer 3

@agent0smith i cant get it -_- ive tried everything...

Answer 4

like what?

Answer 5

What did you try?

Answer 6

i just tried to substitute all the posible answres with -3 and if i got -6 that would be the answer but none of the answers were -6

Answer 7

i also tried to get the vertex for each posible answer but that didnt work either bcs all the vertexs werent the same as the graph

Answer 8

Well, it's concave down, so it's basically between the last two answer choices.

Answer 9

Hold on... vertex form is:
\[y = a(x-h)^2 +k\]where the vertex is (h, k)

Answer 10

Who are you telling to Hold on?

Answer 11

I'm helping her narrow down the choices.

Answer 12

actually i have to find the line of symetry which is -b/2(a) then i have to substitute that for x to find the vertex

Answer 13

The line of symmetry is obvious from the graph.

Answer 14

i have the option of number one and number three do you guys know how i can find the answer?

Answer 15

I already gave you a clue

Answer 16

@Hero i was posting it for her, since i meant to post it earlier... i already helped her narrow down the choices to the last two.

Answer 17

posted earlier "Hint: it can't be either of the first two options, since they both have a positive x^2 term, and the parabola faces down, meaning there must be a negative on the x^2."

Answer 18

im sorry bur both of you are wrong the first and third choices are positive and teh second and fourth are negative so the second and fourth choices coul be right

Answer 19

No, it is impossible for either of the first two choices to be correct.

Answer 20

You just need to learn more about quadratic functions little lady.

Answer 21

OH MY GOSH IM S SORRY I POSTED THE WRONG POSIBLE ANSWERS

Answer 22

That doesn't surprise me

Answer 23

y = -2x2 + 3x + 10
y = x2 + 6x + 10
y = -x2 - 6x - 15
y = 2x2 + 4x + 15

Answer 24

so yeah the first and thrd answers are the possible ones..

Answer 25

we have established that now how do i solve to find which one it is?

Answer 26

Try your substitution of (-3,-6) again

Answer 27

Between number one and number three, one of them should work if those are the correct answer choices.

Answer 28

so substitute the first and the third one with -3 and see if it comes out at -6?

Answer 29

Yes

Answer 30

the first one i came out with 20 and the third one i came out with 12 -_-

Answer 31

im a failure...

Answer 32

You can also just use the axis of symmetry:
\[\frac{ -b }{ 2a }\]whichever one equals -3 is the choice.

Answer 33

Since the axis of symmetry is x= -3 and is given by \[x = \frac{ -b }{ 2a }\]

Answer 34

ok ill try that

Answer 35

ok i do believe it is the third one

Answer 36

-x^2 - 6x - 15
= -(-3)^2 - 6(-3) - 15
= - 9 + 18 - 15
= -9 - 15 + 18
= - 24 + 18
= - 6

Answer 37

Watch your signs.

Answer 38

ok so the third one thank you guys so much for the help and i am assuming you both are guys?

Answer 39

Correct. The third has axis of symmetry... \[x = \frac{ -b }{ 2a } =\frac{ -(-6) }{ 2 \times (-1)} = \frac{ 6 }{ -2 } = -3 \]

Answer 40

I'm a guy, but I wouldn't go around assuming things

Answer 41

haha ok i knew you were a guy i didnt know about agent