The terms 140, a, \(560\) are the first, second and third terms, respectively, of a geometric sequence. If a is positive, what is the value of a ?
geometric sequence in general: a, ar, ar^2, ...
where a is the first term and r is the common ratio.
140 = a
560 = ar^2
Divide to get 4 = r^2, or r = 2. So, the second term is 140 * 2 = 280.