Use unraveling method to obtain a closed-form formula for each of the following recurrences your final answer should be a very simple formula involving n. for part (c), you may want to use a formula from calculus for the sum of a finite geometric series. (a) (5 points) r(n)= n-2r(n-2), r(1)= 3, r(2)= 6. (b.) (5 points) s(n) s(n -1) +2n +1, s(1)-3 (c.) (5 points) t(n)- 3t(n -1) +8, t(0)-2