The product of the first and the third terms of an arithmetic sequence is 9. If all terms of the sequence are positive integers, what is the fourth term?
F * [F + 2D]==9
F==1 - this is the first term
D ==4 - this is the common difference
Your sequence looks like this:
1, 5, 9, 13, 17, 21, 25........and so on.
The 4th term ==9 + 4 ==13
