You're given the following definition: A (1) = 1 A (n) = A (n 1) +n +1 for n > 1 What's the next step in the backward substitution? A (n 1) = A (n 2) +n +1 A (n 1) = A (n 2) + 2n A (n 1) = A (n 2) +n None of the other choices are correct. A (n 1) = A (n 2) + (n 1) A (n 1) = A (n 2) + 2n + 1