Question

What is the sum of the geometric sequence 1, -6, 36, … if there are 7 terms?

Answer 1

6S = 6, -36, 216, ... r^(n-1), -r^n
+S = 1, -6, 36, -216, ...-r^(n-1)
-----------------------------
7S = 1 - r^n

S = (1-r^n)/7

r = -6, n=7

Answer 2

so it would be 6665

Answer 3

in general;

1-r^n
----- ; is the sum of a geometric series
1-r

Answer 4

so if it was out of 6 terms instead would my answer just be -6665 or 39991

Answer 5

hmm, id have to brute it to be sure :) the r=-6 is throwing me off

Answer 6

theses are the 4 questions---What is the sum of the geometric sequence -1, 6, -36, … if there are 7 terms?
A) -39,991
B) -6,665
C) 6,665
D) 39,991
26.
What is the sum of the geometric sequence -1, 6, -36, … if there are 6 terms?
A) -39,991
B) 6,665
C) -6,665
D) 39,991
27.
What is the sum of the geometric sequence 1, -6, 36, … if there are 6 terms?
A) -39,991
B) 6,665
C) -6,665
D) 39,991
28.
What is the sum of the geometric sequence 1, -6, 36, … if there are 7 terms?
A) -39,991
B) -6,665
C) 6,665
D) 39,991

Answer 7

1 S = (-6)^0 +(-6)^1 +(-6)^2 +(-6)^3 +(-6)^4 +(-6)^5
-(-6)S = -(-6)^1 -(-6)^2 -(-6)^3 -(-6)^4 -(-6)^5 - (-6)^6
-----------------------------------------------------------
7S = 1 - (-6)^6

S = (1-(-6)^6)/7

Answer 8

so the geometric seq is the same, all that changes are the number of terms

Answer 9

n is the number of terms; yes

Answer 10

so wld the answers be a,b,d,b

Answer 11

if thats what the calculator pops out, then yes

Answer 12

the 3rd one is the negative of the 2nd one; so thats C i believe

Answer 13

and the last is the negative of the first; so D on that

Answer 14

thanks soo muchhh

Answer 15

yw