Question

What is the sum of a 6-term geometric series if the first term is 20 and the last term is 336,140?

Answer 1

try finding the common ratio r, then use series formula

Answer 2

how do you find the common ratio?

Answer 3

\(a = 20\)

\(t_n = ar^{n-1}\)

Answer 4

6th term = 336,140

\( t_6 = ar^{6-1}\)

\( 336140 = 20r^{5}\)

Answer 5

you can find r ?

Answer 6

To find r, do we divide that big number by 20?

Answer 7

yes

Answer 8

\(\frac{336140}{20} = r^{5}\)

Answer 9

you may use your calculator

Answer 10

so it would be 20 1-16807^6/1-16807?

Answer 11

close ! but the r you got is incorrect !

Answer 12

\(\frac{336140}{20} = r^{5}\)\(\)

\(16807 = r^5\)

\(7^5 = r^5\)

\(7 = r\)

Answer 13

plugin r = 7, in the series formula and find the sum...

Answer 14

How did you get 7^5 from 16807?

Answer 15

16807 = 7x7x7x7x7 = 7^5

ive used my calculator

Answer 16

thank you!

Answer 17

np :)