Question

What is the sum of an 8–term geometric series if the first term is 13 and the last term is –3,639,168?

Answer 1

ok first term is
\[a=13\]
last term is
\[13r^8=–3,639,168\] solve for r by dividing by 13 to get -279936 so
\[r^7=-279936\]
\[r=\sqrt[7]{-279936}=-6\] so now we have r

Answer 2

i meant
\[13r^7= –3,639,168\]

Answer 3

so now use the formula for summing a geomtric series. i think it is
\[\frac{a(r^8-1)}{r-1}\] but you should check it
if so i get
\[\frac{13((-6)^8-1)}{-7}\] lets see

Answer 4

I got –3,119,285

Answer 5

calculator give me
\[-3119285\] so at least it is a nice integer

Answer 6

me too!

Answer 7

Yay! Thank you so much satellite :) you are my hero!! Could you help me with one more?

What is the sum of a 6–term geometric series if the first term is 19 and the last term is 319,333?