Answer:
It seems that Shanna made an error in writing the formula. The given sequence 2, 5, 12.5, 31.25, … seems to be following a geometric progression where each term is obtained by multiplying the previous term by 2.5.
The correct formula should be f(x) = 2 * (2.5)^(x-1) for x ≥ 1, given that f(1) = 2. This formula represents the sequence correctly, where each term is obtained by multiplying the previous term by 2.5.
Therefore, the error Shanna made was in writing the formula f(x + 1) = 2.5f(x).