Question

What is the sum of a 6-term geometric sequence if the first term is 11, the last term is –11,264 and the common ratio is –4?

Answer 1

hey its august wh are you doin homework

Answer 2

i take summer classes so i can get ahead.

Answer 3

formula for the sum of geo is:\[a_1\frac{1-r^n}{1-r}\]

Answer 4

a=11, R=-4, and n=6

Answer 5

yep

Answer 6

so a1=1-(-4)^6/1-(-4)?

Answer 7

hmm, close

a1(1-(-4)^6)/1-(-4)

11(1-(-4)^6)/(1+4)

Answer 8

\[11\frac{1-(-4)^6}{1+4}\]

Answer 9

okay, and this makes the sun?

Answer 10

..... it seems right to me :)

Answer 11

-9009; and since the terms are few in number we can double check with brute math if need be

Answer 12

okay thanks!!!!!!

Answer 13

11 + 11(-4) + 11(-4)^2+ 11(-4)^3+ 11(-4)^4+ 11(-4)^5

11( 1 - 4 + 16 - 64 + 256 - 1024)

11( 273 - 1092)

11( -819)

-819
-819
-------
-9009