I have a problem with finding the sum of this geometric series. (the characters in italics are supposed to be smaller)
a1 = 2, a6 = 486, r = 3
So, applying the sum formula:
Sn = a1 (1 - r^n) / 1 - r
Sn = 2 (1 - 3^n) / 1 - r
I don't have n to figure it out with this formula, instead I have a6, the 6th term. What am I supposed to do with that?
Hello, BlueStar!
Is that the original wording of the problem? . . . It is truly strange.
. . There is too much information.
If the first term is: and the common ratio is:
. . we can use: . and find that: .
If the first term is: and the sixth term is:
. . then: .
If the sixth term is: and the common ratio is:
. . then: .
That is, with two of the facts, we can determine the third.
. . So why gives redundant statements?
On the other hand, they didn't tell us how many terms are in the series.
. . Did I say "strange"? .I meant silly.