SOLUTION: Find the 1st term of this geometric sequence - 3 , 17

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Question 969778: Find the 1st term of this geometric sequence - 3 , 17
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
We need more information than that.
Is 3 the second term, and 17 the third term?

If it is a geometric sequence, then each term is the one before times a fixed number, r .
That number r is called the common ratio, because it is the ratio between any two consecutive terms.
So, term number n%2B1 , b%5Bn%2B1%5D ,
is related to the previous term,
term number n=b%5Bn%5D,
by b%5Bn%2B1%5D=b%5Bn%5D%2Ar<--->r=b%5Bn%2B1%5D%2Fb%5Bn%5D
for all natural number (counting number) values of n .
IF 3 and 17 are consecutive terms,
then the common ratio between consecutive terms is
r=17%2F3 .
Each term is 17%2F3 times the one before.
IF 3 and 17 are the 2nd and 3rd terms respectively,
then b%5B2%5D=3 , b%5B3%5D=17 , r=17%2F3 , and b%5B1%5D is the first term that we want to find.
From b%5Bn%2B1%5D=b%5Bn%5D%2Ar , for n=1 , we get
b%5B1%2B1%5D=b%5B1%5D%2Ar--->b%5B2%5D=b%5B1%5D%2817%2F3%29--->3=b%5B1%5D%2817%2F3%29
so --->b%5B1%5D%2817%2F3%29=3--->b%5B1%5D=3%2F%28%2817%2F3%29%29--->b%5B1%5D=3%283%2F17%29--->b%5B1%5D=9%2F17