For problems 15 and 16, describe and correct the error in writing the explicit rule for the nth term of the geometric sequence for which a, = 3 and r = 2. 15) an = arn 16) an = ra,0-1 an = 3(2)" an = 2(3)0-1 For problems 17 -21, write a rule for the not term of the geometric sequence that has the two given terms. 17) a3 = 10, as = 270 18) a = 1, as = 625 19) a2 = -24, as = 1536 20) a4 = 162, a7 = 4374 21) a, = 2, as = 22) A regional soccer tournament has 64 participating teams. In the first round of the tournament, 32 games are played. In each successive round, the number of games decreases by one half. Find an explicit rule for the number of games played in the nth round. For what values of n does your rule make sense? How many rounds are there