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JEE Main 2021
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

The proposition p \to ~ (p \wedge ~q) is equivalent to :

Options

Solution

Key Concepts and Formulas

  • Implication: pqpqp \to q \equiv \sim p \vee q
  • De Morgan's Law: (pq)pq\sim (p \wedge q) \equiv \sim p \vee \sim q
  • Associative Law: p(qr)(pq)rp \vee (q \vee r) \equiv (p \vee q) \vee r

Step-by-Step Solution

Step 1: Rewrite the implication using the implication equivalence. We want to simplify p(pq)p \to \sim (p \wedge \sim q). Using the implication rule pqpqp \to q \equiv \sim p \vee q, we can rewrite the given expression as: p(pq)p(pq)p \to \sim (p \wedge \sim q) \equiv \sim p \vee \sim (p \wedge \sim q) The reason for doing this is to get rid of the implication and work with conjunctions, disjunctions, and negations, which are easier to manipulate.

Step 2: Apply De Morgan's Law. Now, we apply De Morgan's Law to the term (pq)\sim (p \wedge \sim q). De Morgan's Law states that (pq)pq\sim (p \wedge q) \equiv \sim p \vee \sim q. Therefore: (pq)p(q)pq\sim (p \wedge \sim q) \equiv \sim p \vee \sim (\sim q) \equiv \sim p \vee q Substituting this back into the expression from Step 1, we get: p(pq)p(pq)\sim p \vee \sim (p \wedge \sim q) \equiv \sim p \vee (\sim p \vee q) The reason for this step is to further simplify the expression by removing the conjunction within the negation.

Step 3: Apply the Associative Law. Since the expression now only contains disjunctions, we can apply the associative law, which states that p(qr)(pq)rp \vee (q \vee r) \equiv (p \vee q) \vee r. In our case, this means: p(pq)(pp)q\sim p \vee (\sim p \vee q) \equiv (\sim p \vee \sim p) \vee q The associative law allows us to regroup the terms without changing the meaning of the expression.

Step 4: Simplify the expression using the idempotent law. The expression (pp)(\sim p \vee \sim p) is equivalent to p\sim p because pppp \vee p \equiv p. Therefore: (pp)qpq(\sim p \vee \sim p) \vee q \equiv \sim p \vee q This simplification is crucial to arriving at the final answer.

Common Mistakes & Tips

  • Remember the implication rule: pqpqp \to q \equiv \sim p \vee q. This is fundamental to solving these types of problems.
  • Be careful when applying De Morgan's Law. Remember to negate each term inside the parentheses and change the conjunction to a disjunction (or vice versa).
  • Don't forget the associative and commutative properties of logical operators, as they can simplify the expression.

Summary

We started with the expression p(pq)p \to \sim (p \wedge \sim q) and used the implication rule to rewrite it as p(pq)\sim p \vee \sim (p \wedge \sim q). Then we applied De Morgan's Law to simplify the negated conjunction, resulting in p(pq)\sim p \vee (\sim p \vee q). Finally, using the associative and idempotent laws, we simplified the expression to pq\sim p \vee q.

Final Answer The final answer is \boxed{(\sim p) \vee q}, which corresponds to option (A).

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