8. Find the first 6 terms and the 12th term of the sequence. by =5 and D* = 20 * - 1, for k = 2 9. The following sequences are either arithmetic or geometric. Find an explicit formula for the nth term. State the common difference or ratio. a. -5, -1, 3, 7.. b. by =7 and D, = (1/4)D, _, for n =2 10. Find the sum of the terms of the arithmetic sequence. -11, -8, -5, -2, 1, 4, 7, 10 11. Find the sum of the terms of the geometric sequence. -3, -1, -1/3, -1/9, -1/27 12. Determine whether the geometric series converges. If it does, find its sum. Z 3(0.5)* k =1