Question

What is the sum of the geometric sequence -4, 28, -196, if there are 6 terms?

My answer:
-9,604

Answer 1

what formula did you use?

Answer 2

wht value of r you got ?

Answer 3

an = 1 r n-1

Answer 4

thats not correct formula for SUM

Answer 5

\[an=(-4)(7)^{n-1}\] this is what i got

Answer 6

OH do i use the arthemtic

Answer 7

arithmetic

Answer 8

no...use geometric only, but sum formula

Answer 9

i have the formula now

Answer 10

yes thanks

Answer 11

\(\huge S_n = a_1 \dfrac{r^n-1}{r-1}\)

Answer 12

ok

Answer 13

a1 = 1st term

Answer 14

yes, so a1=... ?
r=... ?

Answer 15

you want sum of 6 tems, so n=6

Answer 16

-4 = a1

Answer 17

yes

Answer 18

r=.... ?

Answer 19

let me think

Answer 20

a2/a1?

Answer 21

divide 2nd term by 1st term*

Answer 22

28/-4

Answer 23

= -7

Answer 24

yes, r=-7
now just plug in values.

Answer 25

ok ill tell you my answer

Answer 26

-42.8571428571

Answer 27

no....

Answer 28

plugged this in: -7(6)-1/-7 - 1

Answer 29

-43/-8?

Answer 30

you missed a1 =-4
also, don't forget about brackets
-4 [(-7)^6-1] / [-7-1]

Answer 31

5.375

Answer 32

oh my error

Answer 33

what is (-7)^6=... ?

Answer 34

117649

Answer 35

my calc doesn't allow me to plug in what you told me

Answer 36

yes, so
-4 [117648]/ (-8) = 117648/2 =... ?

Answer 37

514706

Answer 38

58824

Answer 39

thank you:)))

Answer 40

yes, i too get 58824

Answer 41

welcome ^_^

Answer 42

love u

Answer 43

love you too <3