On a recent homework assignment, Nati needed to solve this equation completely. He incorrectly wrote "zequals9." Solve the equation. What error did Nati make? (z^2 = 81)

The correct solution to the equation z^2 = 81 is z = ±9.

Nati's error was that he only found one solution (z = 9) instead of recognizing that there are two possible solutions, z = 9 and z = -9.