Question

can some check my work plz? What is the sum of a 6-term geometric sequence if the first term is 11, the last term is –11,264 and the common ratio is –4? The answer I got waz 9009? is this right?

Answer 1

can u help me?

Answer 2

im getting -9009

Answer 3

can you explain why plz? :)

Answer 4

ya sure.. .first can you show ur steps. which formula u used

Answer 5

okay. I used sn=a1 1-rn/1-r is the formula I used , and then I replaced 11=a1 , -4=r the 6=n

Answer 6

11*1-(-4)^6/1-(-4)

Answer 7

ok. so far it looks good

Answer 8

then I subtracted the one from what I got (-4)^6 which is =4096/0ver 5

Answer 9

the 5 is from 1-(-4)

Answer 10

yep wait a sec

Answer 11

okay.

Answer 12

so you got this :
11 * (1-4096)/5

Answer 13

right ?

Answer 14

yes.

Answer 15

continue... next step

Answer 16

then I 11*4095/5 which = 45045/5 which =9009?

Answer 17

how is
1-4096 = 4095

?

Answer 18

huh?

Answer 19

it should be
-4095

see ?

Answer 20

and after I do that, I solve like I just did?

Answer 21

yes.
thats the only sign part you did wrong.. rest everything is fine :)

Answer 22

lol, I'm an idiot. Thanks :D

Answer 23

lol.. you did very good :DD

Answer 24

thanks again you were a big help ;)

Answer 25

np... :)