Question

Please help..I need to pass this.
What is the sum of the geometric sequence 1, 3, 9, ... if there are 11 terms?

29,524
55,987
87,381
88,573

I added everything up and got D. But, I searched the question to be sure..and others said A. Which confuses me. I need confirmation, thank you!

Answer 1

⇒S=a×1−rn1−r

substitute r with 3(we're multiplying 3 everytime), n with 11.

Answer 2

a is the first term aka 1.

Answer 3

sum of a geometric series = a X ( 1- r^n)/(1 - r)
here a = 1
r = 3 and n=11
sum = 1 X 1 - 3^11/(1-3) = 1- 3^11/-2 =1- 177147 = - 177146/-2 =?

Answer 4

88,573

Answer 5

So, i was correct?

Answer 6

yes

Answer 7

Yes that is the right answer ^.^
Not sure about how A got in there..

Answer 8

Okay thank you. Can you guys help with another?

Answer 9

sure

Answer 10

oh could i have medal pls

Answer 11

I'll put it in another question and if you help me I'll give you the medal. One sec