Question

I just need a little bit of help with this..

Answer 1

How do I figure out what "r" is?

Answer 2

r is your ratio between the terms.

Answer 3

Ohh, could you show me how to get the ratio?

Answer 4

Do you have a specific problem in mind?

Answer 5

divide a2 by a1 to get your ratio

Answer 6

Okay! one second

Answer 7

I got -0.16 and the 6 goes on continuously

Answer 8

-1/6 basically.

Answer 9

input your values into the formula now

Answer 10

\[\huge S_8 = \frac{ \frac{ -1 }{ 6 } (1+(\frac{ 1 }{ 6 })^8) }{ 1+\frac{ 1 }{ 6 } }\]

Answer 11

its plus because
1 -(-1/6) = 1 + 1/6

Answer 12

823543/6?

Answer 13

how did you get that?

Answer 14

Isn't a1 = -1/6 ?..

Answer 15

wait I'm sorry, that's not right

Answer 16

okay I'm still getting big numbers...but it's (1(1 - (-1/6)^8)/1 - (-1/6) I calculated wrong the first time, this time I got 239945/10077696..

Answer 17

Ah, so the first term is 1 not -1/6, mb.

Answer 18

you should be getting 1679617/1959552

Answer 19

you're asked to find the sum right?

Answer 20

Yea

Answer 21

the formula is
\[\huge S_n=\frac{ a_1(1-r^n) }{ 1-r }\]

Answer 22

if a1 = 1
and the ratio is -1/6
then you should get the fraction 1679617/1959552

Answer 23

so it's
S8 = 1(1- (-1/6)^8)/1 - (-1/6) which is
= 1/1679616/7/6
Is that right so far?

Answer 24

1(1679615/1679616) / 7/6

Answer 25

which is just
(1679615/1679616) / 7/6

Answer 26

now do we multiply by 6/7?

Answer 27

yeah

Answer 28

I got 239945/279936

Answer 29

looks right, i dunno why wolfram gave me the wrong calculations at first

Answer 30

haha I'm using wolfram too XD

Answer 31

lol good job though, i put the entire equation at once so it prob made some error

Answer 32

Ohh, I tried putting the numerator in and accidentally made it 1(1- (-1/6)^8 so that messed stuff up

Answer 33

Thank you for your help!