Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge / 2023 / Paper 2 / 1 / b / Solution

The original PDF places complement bars on the second $A$ in each parenthesis and on the final $A$. Thus the first parenthesis is the empty set, whereas the second is the whole sample space. Their union with any further subset is still the whole space:The bars are missing from the local OCR, so using its unbarred expression would give the wrong result.