3. Find an explicit rule for the nth term of the sequence. -3, -15, -75, -375, ... (2 points) O an = 50 -30 + 1 O an = -3 . 50 - 1 O an = 5 . -30 O an = -3 . 50 4. Find an explicit rule for the nth term of a geometric sequence where the second and fifth terms are -12 and 768, respectively. (2 points) O an = 3 . (-4)n + 1 O an = 3 . 40 - 1 O an = 3 . (-4)0 - 1 an = 3 . 405. A certain radioactive isotope has a halfilife of 11 days. If one is to make a table showing the halfilife decay of a sample of this isotope from 32 grams to 1 gram; list the time (in days, starting with t : 0) in the first column and the mass remaining (in grams) in the second column, which type of sequence is used in the first column and which type of sequence is used in the second column? (2 points)