Question

HELP! SO CLOSE TO FINISH!!!


What is the sum of the geometric sequence -3, 18, -108, ... if there are 8 terms?

Answer 1

please explain!!!!!!!

Answer 2

help?????

Answer 3

can you find the common ratio of this series?

Answer 4

the common ratio r is -6 and a1=-3 so the sum will be if there are 8 terms
s8=-3((1-(-6)^8)/1-(-6)=143967

Answer 5

719,835
119,973
-119,973
-719,835
these are the answer choices..

Answer 6

its 719,835 i made a calc eror

Answer 7

can you show me how?

Answer 8

ok

Answer 9

sum=(a(1-r^n)/(1-r)
a=-3
r=-6
n=8
sum=(-3(1-(-6)^8)/(1-(-6))=(-3*(1-1679616))/7=(-3*(-1679615))/7=5038845/7=719835.

Answer 10

Sn=a1(1-r^n)/(1-r) you need to find the a1 the first term in your sequence which is -3 , and the common ratio, then you subst their values in the equation above , so the common ratio is -6
because if we multiply -3 by 6 we get 18 and if we multiply 18 by -6 we get -108 ,
you want to find the 8 terms so n=8 .