Here's the question you clicked on:
NatalieLove
What is the sum of an 8–term geometric series if the first term is 12 and the last term is –3,359,232?
What is the sum of an 8–term geometric series if the first term is 12 and the last term is –3,359,232 nth term = a r ^ ( n - 1 ) 8th term = 12 r ^ ( 8 - 1 ) = –3,359,232 12 r ^ ( 7 ) = –3,359,232 r^7 = -279,936 r = – 6
its not giving me answer when i plug it in
n Σ a r^k = a ( 1 - r^(n+1)) / ( 1 - r ) k=0 7 Σ 12 r^k = 12 ( 1 - ( – 6 ) ^(7+1)) / ( 1 - ( – 6 )) k=0 ...............= 12 ( 1 - ( – 6 ) ^(8)) / 7 ...............= 12 ( 1 - ( 1,679,616 )) / 7 ...............= 12 ( –1,679,615 ) / 7 ...............= –20,155,380 / 7 ...............= –2,879,340