Part 2 (10 points): Prove that Di = O(n") NOTE: for this problem, you may not use any outside formulas. In particular, you can look up online an exact expression for =12, but you are NOT allowed to use that. The whole point of this problem is that, as we saw in lecture, you can figure out that this sum is (n") without needing any complicated formulas. Part 2 (10 points): Prove that Di = O(n") NOTE: for this problem, you may not use any outside formulas. In particular, you can look up online an exact expression for =12, but you are NOT allowed to use that. The whole point of this problem is that, as we saw in lecture, you can figure out that this sum is (n") without needing any complicated formulas