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A truth table is used to test whether $\sim(P\leftrightarrow Q)\equiv(P\wedge\sim Q)$. The verdict is:
Aequivalent, the two columns agree in all four rows
Bequivalent, both columns are contradictions throughout
Cnot equivalent, they differ when $P$ is false, $Q$ true
Dnot equivalent, the two columns differ in every row
Answer & Solution
Correct answer: C. not equivalent, they differ when $P$ is false, $Q$ true
1. Build both columns over the four combinations of $P$ and $Q$.
2. $P\leftrightarrow Q$ is true when $P$ and $Q$ match, so $\sim(P\leftrightarrow Q)$ is true whenever they differ.
3. That makes $\sim(P\leftrightarrow Q)$ true in two rows: $P$ true with $Q$ false, and $P$ false with $Q$ true.
4. But $P\wedge\sim Q$ is true only in the first of those rows.
5. The columns disagree in the row where $P$ is false and $Q$ is true, so the two are not equivalent.
_Source: NECTA ACSEE 2023 Advanced Mathematics 142/2, Question 2: Logic_
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