Question

Find the sum of a finite geometric sequence from n = 1 to n = 5, using the expression −3(4)^n − 1.

1,023
1,223
−1,023
−4,374

Answer 1

\[S _{n} =a _{p} \frac{ 1-r ^{r-p} }{ 1-r }\] use this @yaya090600

Answer 2

how do i plug it in?

Answer 3

\[S_{n} = a_{p}\frac{ 1-r ^{n-p} }{ 1-r}\]

Answer 4

p=1
n= 5
r=4
a1calculate with use expression -3(4)^n -1

Answer 5

not sure why the exponent in the numerator is n-p,
instead of just n

Answer 6

use this formula
\(\Large S_n = a_1 \dfrac{r^n-1}{r-1}\)

a1 = 1st term =-3
r = common ratio = 4

n= 5

Answer 7

but i 'm used \[a_{0}\] first term @hartnn

Answer 8

this how i get this formula

Answer 9

oh!
so p= 0 :)

Answer 10

yup @hartnn

Answer 11

;D

Answer 12

with p=0, our formula are same :)

Answer 13

@hartnn a0 is first term not a1

Answer 14

right, when you start n from 0 and use the formula you posted.

Answer 15

yup @hartnn

Answer 16

a1 is the first term when we start n from 1 and use the formula i posted.

Answer 17

I put A, is that correct?

Answer 18

\[S _{5} = -13 \frac{ 1-4^4 }{ 1-4} =-13\frac{ -255 }{ -3 } =-1105\] the answer will be across @hartnn

Answer 19

thats not one of the choices

Answer 20

so, using my formula
\(S_n = -3 \dfrac{4^5 -1}{4-1} = 1-4^5 = -1023\)

Answer 21

so its C

Answer 22

yup its is @yaya090600 sorry if i was late

Answer 23

Thank you guys so much

Answer 24

@hartnn there sum from n=0 to n=5

Answer 25

there

Answer 26

@@yaya090600 u understand or no ?