Question

PLEASE HELP URGENT ! what is the 7th of the geometric sequence where a1 = 3 and a5 = -768

Answer 1

nothings THAT urgent :/

Answer 2

we should start by remembering the general formula for a geometric sequence

Answer 3

an = a1*r^(n-1)

Answer 4

we know a1, and we know the value when n=5; from this we can grab the r value

Answer 5

can you fill those in for me?

Answer 6

kind of

Answer 7

give it a try, ill know if its right or not :)

Answer 8

the answer is going to be -3,072

Answer 9

it might be, but lets see if we can build up to that

Answer 10

ok

Answer 11

lets fill in what we are given:

a1 = 3 and a5 = -768 when n=5

an = a1 * r^(n-1)

a5 = -786 = 3 * r^(5-1)

-786/3 = r^(4)

-292 = r^(4) , 4rt the whole thing to find r

4rt(-292) = r

as is this is not a possible sequence to me. an even root can be negative across the reals

Answer 12

an even root canNOT .... i passed typing class, honest :)

Answer 13

check your problem and make sure you havent got an error in the post

Answer 14

ok

Answer 15

i got a feeling the a1 = -3 for this to work like you want it to

Answer 16

yeah

Answer 17

it is

Answer 18

4rt(292) = r then this is what we get for r

take the general formula again, knowing this r and n=7

a7 = -3 * (4rt(292))^(6) and a calculator should popout your intended results

Answer 19

can it be 12,288

Answer 20

no

Answer 21

...can what be?

Answer 22

a7 is going to be a negative value

Answer 23

-12,288

Answer 24

adjust for a mismath and i get:

a7 = -3 * 256^(6/4) = -12288 , so yes

Answer 25

can you help me with thi one ?
What is the sum of the geometric sequence -4, 28, -196 ?

Answer 26

why did you think that the answer "is going to be -3,072"?

Answer 27

i hd my ngatives wrng

Answer 28

signs

Answer 29

ah, itll prolly be best to post up a new question with that sum in it; i have to go for now