Obtain CNF of (p -> q) ^ (¬q <-> ¬p) and obtain DNF of (p v q) -> (¬(p v q))
Understand the Problem
The question is asking to obtain the Conjunctive Normal Form (CNF) and Disjunctive Normal Form (DNF) of two logical expressions. This involves applying logical transformations to rewrite the expressions in standard forms used in propositional logic.
Answer
CNF: $ (P \lor \neg X) \land (Q \lor \neg P) \land (P \lor \neg Q) $; DNF: $ P $
Answer for screen readers
CNF: $ (P \lor \neg X) \land (Q \lor \neg P) \land (P \lor \neg Q) $
DNF: $ P $
Steps to Solve
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Identify the logical expressions
The expressions given for transformation are:- For CNF: $(\neg P \rightarrow \neg X) \land (\neg Q \leftrightarrow \neg P)$
- For DNF: $P \lor (Q \land P)$
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Convert implications and biconditionals for CNF
Recall that:- $A \rightarrow B$ is equivalent to $\neg A \lor B$
- $A \leftrightarrow B$ is equivalent to $(A \rightarrow B) \land (B \rightarrow A)$
For the expression $(\neg P \rightarrow \neg X) \land (\neg Q \leftrightarrow \neg P)$, we can rewrite it:
- $\neg P \rightarrow \neg X$ becomes $\neg(\neg P) \lor \neg X \equiv P \lor \neg X$
- $\neg Q \leftrightarrow \neg P$ becomes $(\neg Q \rightarrow \neg P) \land (\neg P \rightarrow \neg Q)$, which simplifies as follows:
- $\neg Q \rightarrow \neg P$ becomes $Q \lor \neg P$
- $\neg P \rightarrow \neg Q$ becomes $P \lor \neg Q$
Putting it all together: $$(P \lor \neg X) \land ((Q \lor \neg P) \land (P \lor \neg Q))$$
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Distribute to achieve CNF
The CNF can be simplified to a conjunction of disjunctions:
$$ (P \lor \neg X) \land (Q \lor \neg P) \land (P \lor \neg Q) $$ -
Simplifying DNF
For the expression $P \lor (Q \land P)$:- Use the distributive property:
$$ P \lor (Q \land P) = P $$
(since if $P$ is true, the entire expression is true regardless of $Q$)
- Use the distributive property:
CNF: $ (P \lor \neg X) \land (Q \lor \neg P) \land (P \lor \neg Q) $
DNF: $ P $
More Information
The CNF form expresses the logical statement as a conjunction of disjunctions, while the DNF form expresses it as a disjunction of conjunctions. The ability to convert between these forms is crucial in propositional logic and digital logic design.
Tips
- Forgetting to distribute properly can result in incorrect CNF or DNF forms.
- Misapplying the implications and biconditionals leading to confusion in rewriting.
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