Question

Find the sum of a finite geometric sequence from n = 1 to n = 8, using the expression −2(3)^n − 1.
1,083

−6,560

−4,374

6,559

Answer 1

@ganeshie8

Answer 2

sum of finite geometric sequence :
\(\huge \frac{a(r^n-1)}{r-1} \)

Answer 3

start by finding the first term \(a\) and the common ratio \(r\) by interpreting given expression :-
\( −2(3)^{n − 1}\)

Answer 4

compare it wid the general term :-
\(ar^{n-1}\)

a = ?
r = ?

Answer 5

a = -2,
r = 3

right ?

Answer 6

idk

Answer 7

oh ok

Answer 8

we just compared :)
plug them in the sum formula

Answer 9

\(\huge \frac{a(r^n-1)}{r-1}\)

a = -2
r = 3
n = 8

plug and feed it to ur calculator

Answer 10

-13120/2=-65560

Answer 11

right? @ganeshie8

Answer 12

http://www.wolframalpha.com/input/?i=-2%283%5E8-1%29%2F%283-1%29

Answer 13

if u mean -6560 then yes :)

Answer 14

Thank You

Answer 15

np :)