Question

what is the sum of a 7-term geometric series if the first term is -11the last term is -171,875 and the common ratioi -5

Answer 1

ok... so the sum of a geometric series is

\[S_{n} = \frac{a(1 - r^n)}{1 - r}\]

you know n = 7, a = -11 and r = -5

just substitute and calculate the answer

Answer 2

which is a again

Answer 3

sorry I don't have my calculator...

Answer 4

no to substitute

Answer 5

a is the 1st term... -11

Answer 6

ILL LET U KNOW WAT I GOT

Answer 7

-13020

Answer 8

umm that seems low

\[S_{7} = \frac{-11 \times (1 - (-5)^7)}{1 - (-5)}\]

I have to go... good luck with it