Question

Use the information given to identify the .... term of the geometric sequence:

Answer 1

\[a _{9}\]

Answer 2

\[a _{9}=5 ...... r=-2\]

Answer 3

\[a _{9}= 2,560...-320...320...-2,560\]

Answer 4

@pitamar

Answer 5

Geometric sequences are of the form:
$$a_n = c \cdot r^n$$
Where \(c\) and \(r\) are constants. We are not told \(c\) but we're told that \(r=-2\).
So we have:
$$a_n = c \cdot (-2)^n$$
Now we are told that \(a_9 = 5\). But we know that:
$$ a_5 = c \cdot (-2)^9$$ Which means:
$$
5 = c \cdot (-2)^9
$$So first step is to find \(c\). Can you do that?

Answer 6

yeah to get?

Answer 7

-2,560

Answer 8

because of those steps

Answer 9

actually i made a error sorry

Answer 10

I am actually sorta confused. I see that in your question you are already told that \(a_9 = 5\)... so what are you supposed to find?

Answer 11

what a9 equals

Answer 12

but you are told \(a_9 = 5\) at the beginning. Is there a mistake there?

Answer 13

no thats supposed to be the equation

Answer 14

Ok, I'm confused. If you're told \(a_9\) then why are you supposed to find it? sorry about that.

Answer 15

you use it for something but no im confused

Answer 16

@SolomonZelman

Answer 17

@welshfella

Answer 18

its saying use that to find it

Answer 19

dont leaveeeee

Answer 20

so what is c?

Answer 21

Well, though the question now seems pointless.... C is the constant that will make
$$
5 = c \cdot (-2)^9
$$ Work. We just have to solve the equation. So we divide both sides by (-2)^9:
$$
\frac{5}{(-2)^9} = c
$$And since \((-2)^9 = -512\):
$$
c = -\frac{5}{512} \\
a_n = -\frac{5}{512} \cdot (-2)^n
$$
But it makes no sense in the question.. we got this because we know what \(a_9\) was... can you get a picture of this question?

Answer 22

how would i do that?

Answer 23

like how do i do that?

Answer 24

Is it from a book or website?

Answer 25

a website

Answer 26

http://www.take-a-screenshot.org/

Answer 27

When you save it in Paint, make sure you save it in format .jpg (also called .jpeg) or .png
Do not save as .bmp (bitmap), it's really heavy...

Answer 28

i took it i think so now what

Answer 29

i dont have paint

Answer 30

How comes? you use mac?

Answer 31

When you have the picture file you can upload it here. There is an 'Attach File' button down here.
What is your operating system then?

Answer 32

when i take the picture where does it go so i can attach it???

Answer 33

It goes to clipboard. you can paste it in programs. Like Paint or Office Word. Do you have any of these?

Answer 34

yes but wheres the clipboard

Answer 35

i just cant find the clipboard

Answer 36

Oh lol. Clipboard is just a name for things you've copied. You know Copy Paste? Ctrl-C Ctrl-V?
So it's like you 'copied' the picture. Now just paste it.

Answer 37

ok

Answer 38

like that?

Answer 39

Yes, very good.
Man... I think this is a mistake in the question lol =\
It makes absolutely no sense...

Answer 40

well what would you guees the answer is cause i have no idea

Answer 41

Sorry the site has stopped working for me.
I think their mistake is that they wrote \(a_9 = 5 \qquad r=-2\) but meant \(c = 5 \qquad r=-2\), because in that case our equation becomes:
$$
a_n = c \cdot r^n = 5 \cdot (-2)^n
$$And:
$$
a_9 = 5 \cdot (-2)^9 = 5 \cdot -512 = -2560
$$Which is one of the answers.