Question

what is 10 subscript 8?

Answer 1

Do you mean superscript?
Cause otherwise, I don't think that has any meaning.

Answer 2

like \[10_{8}\]

Answer 3

What is the context? What sort of math question are you seeing this in?

Answer 4

What is the sum of an 8-term geometric sequence if the first term is 10 and the last term is
781,250? In order to find the common ratio im using the formula \[a _{n}=a _{1}r ^{n-1}\]

Answer 5

so a= 10 and n=8

Answer 6

Ah... gotcha, no \[a_1=10\]
\[a_n\] means the nth term in the sequence.

Answer 7

i thought a and a1 are basically just the same thing? arent they both just the first term?

Answer 8

\[a_8\] means the 8th term, which in this case is 781250. In other words, the first term, 10 is multiplied by some common ratio eight times and the result is 781250.

Answer 9

'a' is the name of the variable. The subscript tells you where in the sequence it is.

Answer 10

do you mind walking me through the equation?

Answer 11

For example: {2, 6, 18, 54} =
\[a_1, a_2, a_3, a_4\] with a1=2 and a common ratio of 3.

Answer 12

If you're using the equation to solve for r, start with
\[a_n=a_1r^{n−1}\] and divide both sides by a1
\[\rightarrow \frac{a_n}{a_1}=r^{n−1}\]

Answer 13

Then r is found by taking the (n-1)st root of a_n/a_1.
In your example, you need to take the 7th root of 751250 ÷ 10.

Answer 14

*sorry 781250 ÷ 10, not 751250. Typo.

Answer 15

You should have another formula available to find the sum of that sequence once you know the common ratio.

Answer 16

i do, thanks! o what the common ratio then?

Answer 17

781250 ÷ 10?

Answer 18

78125?

Answer 19

Yes, so the common ratio is the 7th root of 78125.