Question

Which of these graphs show the quadratic function y = 2x2 + 8x + 7?

A

B

C

D

Answer 1

pick the one with the right vertex first coordinate of the vertex is \(-\frac{b}{2a}\)

Answer 2

tbh i really don't even know how to do that

Answer 3

you have
\[ \large y = \color{red}2x^2 + \color{green}8x + \color{blue}7\]
which looks like
\[ \large y = \color{red}ax^2 + \color{green}bx + \color{blue}c\]

Answer 4

compute\[\large -\frac{\color{green}b}{2\color{red}a}\]

Answer 5

um so would it be A then?

Answer 6

what you you get when you compute
\[\large -\frac{\color{green}8}{2\times \color{red}2}\]?

Answer 7

-8/4

Answer 8

yes, and what is minus eight divided by four?

Answer 9

-2/1

Answer 10

?

Answer 11

oh

Answer 12

what is minus two divided by one?

Answer 13

I just simplified

Answer 14

there is no such mathematical operation as simplify
it is division here
you should get \(-2\)

Answer 15

oh you wanted me divide my bad

Answer 16

so if you get -2 then what's the answer i'm confused?

Answer 17

that means the first coordinate of the vertex is \(-2\) so from your choices that narrows it down to B and C
both have the vertex with first coordinate \(-2\)

Answer 18

so b?

Answer 19

either B or C
you have to find the second coordinate of the vertex to see which one is right

Answer 20

how do you find the second coordinate? i'm sorry I don't mean to be annoying. I just really need to get this right.

Answer 21

no problem
but let me ask you a question
if the first coordinate is \(-2\) i.e. if \(x=-2\) and
\[ \large y = \color{red}2x^2 + \color{green}8x + \color{blue}7\] then how do you think you would find the second coordinate?

Answer 22

plug it in?

Answer 23

zactly!

Answer 24

i.e. compute
\[2(-2)^2+8(-2)+7\]

Answer 25

so -17?

Answer 26

no

Answer 27

go slowly

Answer 28

i still got -17

Answer 29

not sure how
what is \((-2)^2\) ?

Answer 30

-4

Answer 31

ah maybe that is how

Answer 32

\((-2)^2=(-2)\times (-2)=4\)

Answer 33

so now try
\[2\times 4+8\times (-2)+7\]

Answer 34

i'm using a scientific calculator so that's what it said

Answer 35

calculator cannot read your mind
if you typed in \(-2^2\) then you get \(-4\)

Answer 36

ok

Answer 37

-25?

Answer 38

my bad -1

Answer 39

yes that is it \(-1\) making the vertex \((-2,-1)\)

Answer 40

so the final answer is B

Answer 41

yes

Answer 42

Thank you so much

Answer 43

yw