a Let an be the number of divers in the nth ring. To determine a rule for the given geometric sequence, we will use the formula for the .
an=a1rn−1
In our case, since there are
5 divers in the first ring the first term is
a1=5. Because each ring after the first has twice as many skydivers as the preceding ring, its common ratio is
r=2. Next, we will substitute values for
a1 and
r into the explicit rule of geometric sequences.