Question

[9.01] Identify the vertex for the graph of y = 2x2 + 8x − 3.

(2, 21)

(2, 17)

(−2, −11)

(−2, −27)
Can someone help me, because I keep getting (-2, -3) and that's obviously not the answer. So can you guys tell me what you're getting?

Answer 1

Can't you use options?

Answer 2

I'm not to sure what're you talking about, do you mean the question options?

Answer 3

yes, you have provided 4 options to us.

Answer 4

I mean, I have to use the x=-b/2(a) formula to find the x intercept, but every time I plug that into the problem I get something that's not there, so I don't see how I could plug in the options

Answer 5

you are getting \(x\) as \(-2\) ??

Answer 6

Yes

Answer 7

can't we use this equation:
\[y = a(x-h)^2 + k\]

Answer 8

This is for axis of symmetry..

Answer 9

Ive never seen that equation in my class, so I assuming no,I just need help lol, I have been stressing this problem for a while now

Answer 10

That equation is vertex form of the parabola, there \((h,k)\) is the vertex.

Answer 11

Okay tell me how you found y = -3??

Answer 12

I just plugged -2 into the problem, I was taught to do that lol

Answer 13

Let me check it from the vertex form too.. :)

Answer 14

Ok :) I hope i'm not coming off snippy or mean, I am really grateful for your help, it's hard to convey emotions over text.

Answer 15

I found your mistake..

Answer 16

Plug in \(-2\) in the equation back:
\[y = 2(-2)^2 + 8(-2) - 3 \implies y = 8 - 16 - 3 \implies y = -8-3 = ??\]

Answer 17

Getting?

Answer 18

@LeilaA7X found it or not??

Answer 19

Sorry I was doing another problem, lemme work this out

Answer 20

I got -11

Answer 21

For more info, I can tell that we can also find vertex from vertex equation.. I will tell you that how to do that.. Yeah \(-11\) is right.. :)

Answer 22

So the answer is (-2, -11)

Answer 23

And I understand it for the most part, I just had a slip up on this one lol :)

Answer 24

Vertex form just need the concept of completing the square..

Answer 25

Ok, thank you waterineyes!

Answer 26

\[y = a(x-h)^2 + k \\ y = 2x^2 + 8x - 3 \\ \frac{y}{2} = x^2 + 4x - \frac{3}{2} \\ \frac{y}{2} = x^2 + 4x - \frac{3}{2} + (2)^2 - (2)^2 \\ \frac{y}{2} = (x+2)^2 - \frac{11}{2} \\ \color{blue}{y = 2(x+2)^2 - 11}\]

Answer 27

It is just like :

\(y = a(x-h)^2 + k\), comparison gives you : \((h,k) = (-2, -11)\)

Answer 28

you are welcome dear.. :)

Answer 29

I think you will soon learn this too.. :)