1. The problem statement, all variables and given/known data (Uploaded photo from Zettili Quantum Mechanics - Chapter 3 - Solved problems 3.4 and 3.5) Check at problem 3.4 the relation that he gives between operator A and state φn. Now check the relation that he uses in problem 3.5 between A and φn again. They are different while on the announcement of prob 3.5 he does not mention any change of this relation. 2. Relevant equations 3. The attempt at a solution Is there any misprint or am i that dumb that cannot understand some change of the relation that he implies?